Environmental, social, and behavioral challenges of the human circadian clock in real-life conditions.

Urban environments, in which ambient light has become a less-reliable entrainer, are challenging for the biological clock to maintain performance. As a consequence, human circadian rhythms are less robust and more variable among individuals. Assessing the individual phase of entrainment, as well as its plastic shifts in response to disturbances of the physical and social environment, is a way to measure circadian disruption. However, this is still difficult to address in real-life scenarios in which several factors modulate the circadian phase not always in a concerted manner. In this perspective, we present the contribution of two real-life situations, in which the circadian system is challenged by important alterations in entraining signals: 1) a trip to the Antarctic summer (socio-environmental challenge), and 2) dancers trained in morning/night shifts (socio-behavioral challenge). Both natural chronobiological experiments are helpful in exploring the functioning and plasticity of the circadian clock and allow for considering individual characteristics and history.

Epidemiology of sleep patterns and circadian typology in uruguayan children: The contribution of school shifts.

Healthy sleep is defined by the combination of adequate duration, good quality, and regular timing. In children, sleep thus depends on the interplay of individual, parental, organizational, community, and social variables, but only a few studies have addressed this issue in a comprehensive way nationwide. Using the Uruguayan nationally representative survey (Nutrition, Child Development, and Health Survey, Encuesta de Nutrición, Desarrollo Infantil y Salud, ENDIS), we present the first epidemiological characterization of chronobiological and sleep parameters in Latin American children. On average, Uruguayan urban children (n = 2437; 5-10-years old) showed quite late chronotypes (MSFsc = 03:53 ± 1:07), moderate misalignment (SJL = 1.0 ± 0.9 h), and adequate sleep duration (SDweek = 9.9 ± 1.0 h). Further, we show the substantial influence of school shift schedules on children's circadian typology and sleep patterns. Our results show that children attending the morning school shift have a higher risk of sleep problems than afternoon-school shift ones. The chronotype and sleep were earlier in morning-school shift children than in children attending the afternoon school shift. However, morning-school shift children had stronger misalignment, shorter sleep on school days, and a higher risk of chronic sleep deficit and non-healthy circadian misalignment (even worse in late chronotypes) than afternoon-shift children. This evidence points to the need of evaluating policies to reorganize school start times to prevent the negative effects that early schooling seems to have on children's sleep health, which has been neglected so far.

Individual light history matters to deal with the Antarctic summer.

The effect of light, main zeitgeber of the circadian system, depends on the time of day it is received. A brief trip to the Antarctic summer (ANT) allowed us to explore the impact of a sudden and synchronized increase in light exposure on activity-rest rhythms and sleep patterns of 11 Uruguayan university students, and to assess the significance of light history in determining individual circadian phase shift. Measurements collected in the peri-equinox in Montevideo, Uruguay (baseline situation, MVD) and in ANT, included sleep logs, actigraphy, and salivary melatonin to determine dim-light melatonin onset (DLMO), the most reliable marker of circadian phase. The increase in light exposure in ANT with respect to MVD (affecting both light-sensitive windows with opposite effects on the circadian phase) resulted in no net change in DLMO among participants as some participants advanced their DLMO and some others delayed it. The ultimate cause of each participant's distinctive circadian phase shift relied on the unique change in light exposure each individual was subjected to between their MVD and ANT. This study shows an association between the individual light history and the circadian phase shift.

The Influence of Light and Physical Activity on the Timing and Duration of Sleep: Insights from a Natural Model of Dance Training in Shifts.

Environmental, social, and behavioral variables influence sleep timing and duration. Using wrist-worn accelerometers, we recorded 31 dancers (age = 22.6 ± 3.5) for 17 days and who trained either in the morning (n = 15) or in the late evening (n = 16). We estimated the dancers' daily sleep pattern: onset, end, and duration. In addition, their minutes of moderate-to-vigorous physical activity (MVPA) and mean light illuminance were also calculated daily and for the morning-shift and late-evening-shift time windows. On training days, the shifts involved differences in sleep timing, alarm-driven waking frequency, and the pattern of light exposure and MVPA duration. Sleep was strongly advanced when dancers trained in the morning and when alarms were used, while morning light had a low influence. Sleep was delayed when dancers were more exposed to light and displayed longer MVPA during the late evening. Sleep duration was strongly reduced on weekends and when alarms were used. A small reduction in sleep duration was also observed when morning illuminance was lower or when late evening MVPA was longer. Training in shifts influenced the timing of environmental and behavioral factors, which added up to shape dancers' sleep timing and duration.

Evaluation of environmental, social, and behavioral modulations of the circadian phase of dancers trained in shifts.

The interplay of environmental, social, and behavioral factors influencing human circadian phase in ecological conditions remains elusive. The Uruguayan national dance school END-SODRE operating in two shifts (morning: 8:30-12:30 and night: 20:00-24:00) allowed us to evaluate how social demands, chronotype, environmental light, physical activity, and sleep patterns affected individual circadian phase measured by the onset of the nocturnal increase of melatonin (DLMO) in a single study. The DLMO was 1.5 h earlier in morning-shift dancers (n = 7) compared to night-shift dancers (n = 11). Sleep time and chronotype (only in night-shift dancers) were associated with the circadian phase. In training days, during each participant's phase-advance and phase-delay time windows, light exposure was similar between morning and night-shift dancers and did not correlate with DLMO. In contrast, the time spent in moderate-vigorous physical activity during each participant's phase-lag time window was higher in night-shift dancers than in morning-shift dancers and positively correlated with DLMO.

Challenged by extremely irregular school schedules, Uruguayan adolescents only set their waking time.

INTRODUCTION: Early school start times adversely influence adolescents' sleep duration. Late school start times and remote learning are associated with longer sleep durations. We leveraged a highly variable school schedule adopted after the first SARS-CoV-2 wave in Uruguay to study the influence of a hybrid mode of instruction (in-person/remote) with irregular school start times on adolescents' sleep. METHODS: Objective sleep on school nights (120 observations) was determined using accelerometry recordings of 15 high-school students (3 males 15-17 years old). We used mixed-effects regressions to explore the influence of the mode of instruction (in-person/remote) and school start time on adolescents' sleep patterns (onset, end, and duration). RESULTS: An irregular individual regime of 2-6 school days per week, either in-person or remote, and with irregular start times (range: 07:30-12:00) were observed during the studied period. Remote learning delayed sleep end by 48 ± 9 min and increased sleep duration by 36 ± 12 min. In addition, 1 h delay in school start time delayed sleep end in 36 ± 4 min and increased sleep duration in 34 ± 5 min. CONCLUSIONS: A strong linear association of the mode of instruction and the school start time with participants' sleep was observed: Only waking time was associated with both school start time and mode of instruction, and sleep duration increased when students were taught remotely and when school started later. These results add evidence to the effectiveness of delaying school start time to improve adolescents' sleep. However, these efforts may not overcome the influence of a very late circadian orientation, as observed in Uruguayan adolescents.

Bidirectional association between light exposure and sleep in adolescents.

Sleep behaviour is controlled by both circadian and homeostatic influences. Changes in both factors are related to the delayed sleep timing observed in adolescence, which also generates restrictions in their sleep duration. In addition, the circadian factor explains part of the observed influence of light on sleep duration. We recorded 15 high-school students for 23 days (vacation: 11 days; school term: 12 days) using GENEactive accelerometers. We employed a repeated-measures analysis to explore the day-to-day bidirectional association between mean light exposure and sleep behaviour across a period with extreme variability in social pressures. Sleep onset was more than 30 min earlier and sleep duration almost 20 min longer when previous day light was 10 times more intense. Light intensity had a reduction of more than 20% as sleep ended 1 hr later. Besides, sleep onset and offset were both later during vacation than on school days (almost 2 hr and 4 hr, respectively) and free days (almost 1 hr, respectively). Therefore, sleep duration was almost 2 hr longer on vacation and free days than on school days. On the other hand, light exposure intensity was twice as high during vacation days when adjusted by sleep timing. Insufficient sleep duration is a major problem for adolescents. Although we found that light exposure was associated with longer sleep duration, the influence of school start times was greater and ended up prevailing, which explained the short sleep durations observed on school days.

Association of androgens and estrogens with agonistic behavior in the annual fish Austrolebias reicherti.

Agonistic behavior governs the settlement of conflicts among conspecifics for limiting resources. Sex steroids play a critical role in the regulation of agonistic behavior which in turn may produce modulations in hormone titres. In this study we analyzed the association of androgens and estrogens with agonistic behavior in the annual fish Austrolebias reicherti. This native species inhabits temporary ponds that dry out completely during summer, having one of the shortest lifespans among vertebrates. They are highly sexually dimorphic and have a single breeding season during which they reproduce continuously. Here we measured plasma levels of 11-ketotestosterone (11KT) and 17ß-estradiol (E2) in adult males after the resolution of a social conflict and assessed the role of the aromatase conversion of testosterone (T) to E2 in male aggression. Winners had higher levels of 11KT than losers yet; winner 11KT levels did not differ from those of males not exposed to a social challenge. E2 levels did not show differences among winners, losers or control males. However, fights under the aromatase inhibitor Fadrozole were overall less aggressive than control fights. Our results suggest an androgen response to losing a conflict and that the conversion of T to E2 is involved in the regulation of aggressive behavior. Annual fish extreme life history may give new insights on hormone-behavior interactions.

Should I study or should I go (to sleep)? The influence of test schedule on the sleep behavior of undergraduates and its association with performance.

Sleep is crucial for college students' well-being. Although recommended sleep duration is between 7-9 hours per day, many students do not sleep that much. Scholar demands are among the causes of observed sleep deprivation in youth. We explored the influence of having a school test on previous night sleep in first-year students and the association of sleep duration and test performance. We ran two surveys in freshman students of the Universidad de la República, Montevideo, Uruguay: 1) 97 students of the School of Sciences who took the test at the same time; and 2) 252 School of Psychology students who took the test in four successive shifts. More than 1/2 of the participants (survey #1) and almost 1/3 (survey #2) reported short regular sleep duration (< 7h). In both samples, the sleep duration of the night before the test was reduced with respect to regular nights (survey #1: 2.1 ± 0.2 h, p < 0.001; survey #2: between 1.7 ± 0.4 h and 3.6 ± 0.3 h, all p < 0.001), with more than 10% of the students who did not sleep at all. In survey 2, sleep duration increased in later shifts (F (3,248) = 4.6, p = 0.004). Using logit regressions, we confirmed that sleep duration was positively related to test scores in both samples (survey #1: exp B = 1.15, p < 0.001; pseudo-R2 = 0.38; survey #2: exp B = 1.03, p < 0.001; pseudo-R2 = 0.25). Delaying test start time may prevent the reduction in sleep duration, which may also improve school performance. In addition, educational policies should include information for students about the impact of sleep on learning and of the consequences of reduced sleep duration.

Short Sleep Duration and Extremely Delayed Chronotypes in Uruguayan Youth: The Role of School Start Times and Social Constraints.

During adolescence, biological, psychosocial, and contextual factors converge in a "perfect storm" and have been put forward to explain the delay in chronotype observed at this age and the prevalence of disrupted sleep. This study provides evidence to support that chronotype and sleep patterns (particularly sleep duration) are socially constrained and to identify novel significant social predictors. Uruguayan public school activities are arranged in up to 4 shifts, creating a natural experiment to examine the effect of school timing on questionnaire-based assessments of sleep and chronotype. In this study, 268 high school students (15-18 years old) who attended school either on morning (0730 to 1130 h) or afternoon shifts (1130 h to 1530 h) responded to an adapted School Sleep Habits Survey. Students attending afternoon shifts had later chronotypes (a 1.5-h later midpoint of sleep on free days adjusted for sleep debt) than those attending the morning shift. Besides shift, evening social activities (including dinner time) were further identified as key predictors of late chronotypes, whereas age and gender were not. Sleep on school days was overall advanced and reduced with respect to weekends, and these effects were stronger in morning-shift students. Weekend sleep duration was similar between shifts, which probably caused the prevalence of reduced sleep durations (average weekly sleep duration, SDweek <8 h) to be higher in morning-shift students (almost 80%) than in afternoon-shift ones (34%). Reduced sleep duration was significantly higher in morning-shift students. In addition, age, chronotype, and dinner time became relevant determinants of sleep deficit only in the morning-shift students. Besides the important social constraint of early school start time, this is the first study to confirm the significance of other types of social pressures on both adolescents' chronotype and sleep deficit, which can be useful as potential new targets for effective policies to protect adolescent sleep.

Female and male rufous horneros eject shiny cowbird eggs using a mental template of the size of their own eggs.

Hosts of interspecific brood parasites often evolve antiparasitic defences, like the recognition and rejection of parasite's eggs. Most hosts use differences in coloration and maculation to discriminate between their own and parasitic eggs, but there are a few cases of hosts using the size of eggs as a cue. To recognize parasite eggs, hosts may require the presence of their own eggs and use a discordancy rule or may use a mental template of their own eggs. Females are responsible for egg rejection in hosts in which they incubate alone, but if incubation is shared, males can also reject parasitic eggs. The rufous hornero, Furnarius rufus, a host of the shiny cowbird Molothrus bonariensis, ejects parasite eggs using egg size as a cue. We studied the cognitive mechanism underlying the recognition and ejection of parasitic eggs by this host. We experimentally parasitized hornero nests with eggs of different size, with and without the presence of host eggs and determined which sex was responsible for the ejection. We found that horneros ejected parasitic eggs using the size of the egg as a cue and did not need to compare parasitic eggs with their own eggs, which is consistent with the hypothesis of a mental template. Females and males ejected eggs at similar frequencies. We also found that cowbird eggs laid in hornero nests were longer and wider than those laid in nests of other host in the same area, which is consistent with the hypothesis of host-specific female cowbird lineages evolving larger eggs to deceit horneros from recognizing and ejecting their eggs.

Chronotype-Dependent Changes in Sleep Habits Associated with Dim Light Melatonin Onset in the Antarctic Summer.

Dim light melatonin onset (DLMO) is the most reliable measure of human central circadian timing. Its modulation by light exposure and chronotype has been scarcely approached. We evaluated the impact of light changes on the interaction between melatonin, sleep, and chronotype in university students (n = 12) between the Antarctic summer (10 days) and the autumn equinox in Montevideo, Uruguay (10 days). Circadian preferences were tested by validated questionnaires. A Morningness-Eveningness Questionnaire average value (47 ± 8.01) was used to separate late and early participants. Daylight exposure (measured by actimetry) was significantly higher in Antarctica versus Montevideo in both sensitive time windows (the morning phase-advancing and the evening phase-delaying). Melatonin was measured in hourly saliva samples (18-24 h) collected in dim light conditions (<30 lx) during the last night of each study period. Early and late participants were exposed to similar amounts of light in both sites and time windows, but only early participants were significantly more exposed during the late evening in Antarctica. Late participants advanced their DLMO with no changes in sleep onset time in Antarctica, while early participants delayed their DLMO and sleep onset time. This different susceptibility to respond to light may be explained by a subtle difference in evening light exposure between chronotypes.

School start times matter, eveningness does not.

Morningness-Eveningness (M-E) has been associated with school performance when school activities are arranged early in the morning. This study aims to evaluate this association in 224 adolescents of a secondary school in Montevideo, Uruguay, attending either morning or afternoon shifts. Students' socio-demographic characteristics and performance indicators were similar across shifts, while afternoon-shift students exhibited later circadian preferences. After controlling for socio-demographic and other educational variables, eveningness was associated with lower grades only in morning-shift students. Our study suggests that eveningness influence on school performance is contingent on the temporal arrangement of scholar activities.

Females of the annual killifish Austrolebias reicherti (Cyprinodontiformes: Rivulidae) recognize conspecific mates based upon chemical cues.

Olfactory abilities to discriminate conspecifics can be determinant to prevent hybridization between closely-related species in many taxa. Annual killifish Austrolebias reicherti and A. charrua are sister species inhabiting temporary ponds within Eastern Wetlands of Uruguay with an overlapping area in their distributions. Herein, we assess species recognition sensory abilities in females of A. reicherti in classic dual-choice tests. We exposed two different groups of females, one to olfactory but not visual cues, and the other to visual but not olfactory cues, from conspecific and heterospecific A. charrua males. Austrolebias reicherti females preferred conspecific males when based solely on olfactory cues, and showed no discrimination when exposed to visual traits only. Austrolebias inhabit shallow, muddy and highly turbid ponds that may promote the use of non-visual cues. Although preliminary, the results of this study suggest the importance of chemical communication in species mate recognition in A. reicherti and points annual fishes as a promising model to study the role of mate choice in reproductive isolation and speciation.

Extreme late chronotypes and social jetlag challenged by Antarctic conditions in a population of university students from Uruguay.

In humans, a person's chronotype depends on environmental cues and on individual characteristics, with late chronotypes prevailing in youth. Social jetlag (SJL), the misalignment between an individual׳s biological clock and social time, is higher in late chronotypes. Strong SJL is expected in Uruguayan university students with morning class schedules and very late entertainment activities. Sleep disorders have been reported in Antarctic inhabitants, that might be a response to the extreme environment or to the strictness of Antarctic life. We evaluated, for the first time in Uruguay, the chronotypes and SJL of 17 undergraduate students of the First Uruguayan Summer School on Antarctic Research, using Munich Chronotype Questionnaire (MCTQ) and sleep logs (SL) recorded during 3 phases: pre-Antarctic, Antarctic, and post-Antarctic. The midsleep point of free days corrected for sleep debt on work days (MSFsc,) was used as proxy of individuals' chronotype, whose values (around 6 a.m.) are the latest ever reported. We found a SJL of around 2 h in average, which correlated positively with MSFsc, confirming that late chronotypes generate a higher sleep debt during weekdays. Midsleep point and sleep duration significantly decreased between pre-Antarctic and Antarctic phases, and sleep duration rebounded to significant higher values in the post-Antarctic phase. Waking time, but not sleep onset time, significantly varied among phases. This evidence suggests that sleep schedules more likely depended on the social agenda than on the environmental light-dark shifts. High motivation of students towards Antarctic activities likely induced a subjective perception of welfare non-dependent on sleep duration.

Seasonal variation in female mate choice and operational sex ratio in wild populations of an annual fish, Austrolebias reicherti.

The intensity of mating competition and the potential benefits for female of mating with certain males can be influenced by several extrinsic factors, such that behavioral decisions can be highly context-dependent. Short-lived species with a single reproductive season are a unique model to study context-sensitive mating decisions. Through exhaustive sampling in the field and simultaneous choice tests in the laboratory, we evaluated operational sex ratio (OSR) and female mate choice at the beginning and end of the reproductive season in the annual killifish Austrolebias reicherti. We found seasonal change in both OSR and female mate choice. At the start of the reproductive season the OSR did not deviate from parity, and females preferred larger males. Later in the reproductive season, while the proportion of males in the ponds decreased, females became unselective with respect to male size. The particular biological cycle of annual killifish, where both life expectancy and mating opportunities decline sharply over a short timescale, could account for the seasonal change in female choice. Reduction in choosiness could arise from diminished reproductive prospects due to a decline in male availability. Moreover, as the end of the season approaches, any benefits of choosiness are presumably reduced: a female's fitness will be higher if she mates with any male than if she forgoes reproduction and dies. Future work will disentangle the mechanisms underlying seasonal changes in mating preferences, notably direct responses to demographic factors, environmental cues, or intrinsic changes during development.

Intra- and intersexual selection on male body size in the annual killifish Austrolebias charrua.

Since many traits are involved in both female mating decisions and male contest outcomes, female mate choice and male competition can act in concert to intensify sexual selection on male traits, or in opposition to weaken it. In the sexually dimorphic annual killifish, Austrolebias charrua, we evaluated the effect of male body size on female mate choice, male-male competition, and their interaction. We carried out an experiment with three consecutive stages: (i) female choice test between males of different size in a classic two-choice device, (ii) agonistic interactions between males used in the previous stage, and (iii) a second female choice test to evaluate preference consistency in females that either were allowed or were prevented from observing the male competition. Larger males were preferred by females and became socially dominant in agonistic interactions. Further, females were consistent in their choices, and this consistency was independent of whether they had observed or not the male contest. Our research shows that, in A. charrua, intrasexual competition and female mate choice act in concert with respect to male body size. The unique life-history of Austrolebias and the high repeatability of mate-choice assays make this system a promising candidate for studies of behavioural evolution.

Comportamiento maternal de Arctocephalus Australis, en Isla de Lobos - Uruguay / Maternal behavior of Arctocephalus Australis, in Isla de Lobos - Uruguay

Comportamiento maternal de Arctocephalus australis, En los mamíferos, generalmente las hembras realizan el cuidado de la progenie repartiendo su inversión entre las crías presentes y futuras, maximizando la relación costo-beneficio. La variación en los comportamientos del cuidado maternal puede afectar en forma diferencial la supervivencia de las crías. A. australis se presenta como un interesante modelo para evaluar la incidencia de los diferentes componentes del cuidado maternal en la supervivencia del cachorro e investigar la ocurrencia de variación mensual y diaria de los comportamientos madre-cría. Diariamente se registró la presencia de hembras marcadas en la colonia mediante muestreos focales y de barrido. La frecuencia de los estados y eventos comportamentales variaron entre los meses de muestreo. Los viajes de alimentación de las madres exhibieron una duración muy variable, y el patrón de viajes-asistencia así como la permanencia de la madre con su cría incidieron en la supervivencia de los cachorros. Los resultados se discuten enmarcados en diferentes hipótesis(AU)

In mammals, paternal care is usually performed by females, dividing their investment between present and future offspring and maximizing the cost-benefit relationship. Variation in maternal care behaviour can affect pups’ survival differentially. A. australis is an interest model to assess the incidence of different components of maternal care behaviour on pups’ survival, as well as the monthly and daily variation in mother-calf behaviour. The presence of marked females at the rookery was recorded using focal and scanning sampling methods. State and event frequencies changed between months. Feeding trips had highly variable duration and the survival was strongly affected by the foraging cycle strategy used and the mother-pup contact recorded. The results are discussed in the frame of different hypotheses(AU)

Comportamiento maternal de Arctocephalus Australis, en Isla de Lobos - Uruguay / Maternal behavior of Arctocephalus Australis, in Isla de Lobos - Uruguay

Comportamiento maternal de Arctocephalus australis, En los mamíferos, generalmente las hembras realizan el cuidado de la progenie repartiendo su inversión entre las crías presentes y futuras, maximizando la relación costo-beneficio. La variación en los comportamientos del cuidado maternal puede afectar en forma diferencial la supervivencia de las crías. A. australis se presenta como un interesante modelo para evaluar la incidencia de los diferentes componentes del cuidado maternal en la supervivencia del cachorro e investigar la ocurrencia de variación mensual y diaria de los comportamientos madre-cría. Diariamente se registró la presencia de hembras marcadas en la colonia mediante muestreos focales y de barrido. La frecuencia de los estados y eventos comportamentales variaron entre los meses de muestreo. Los viajes de alimentación de las madres exhibieron una duración muy variable, y el patrón de viajes-asistencia así como la permanencia de la madre con su cría incidieron en la supervivencia de los cachorros. Los resultados se discuten enmarcados en diferentes hipótesis

In mammals, paternal care is usually performed by females, dividing their investment between present and future offspring and maximizing the cost-benefit relationship. Variation in maternal care behaviour can affect pups’ survival differentially. A. australis is an interest model to assess the incidence of different components of maternal care behaviour on pups’ survival, as well as the monthly and daily variation in mother-calf behaviour. The presence of marked females at the rookery was recorded using focal and scanning sampling methods. State and event frequencies changed between months. Feeding trips had highly variable duration and the survival was strongly affected by the foraging cycle strategy used and the mother-pup contact recorded. The results are discussed in the frame of different hypotheses

Reproductive behavior in the annual fish Austrolebias reicherti Loureiro & García 2004 (Cyprinodontiformes: Rivulidae)

Annual fishes inhabit temporary ponds that dry out seasonally and the adaptations to survive this extreme condition include high metabolic rates and an elaborate courtship behavior which ends in the deposition of drought-resistant eggs, capable of going through diapause stages in the substrate. The pronounced sexual dimorphism that these fishes show suggests that sexual selection could play a key role in the differentiation, speciation and evolution of this diverse group of fishes. However, there is scarce information about their reproductive isolation mechanisms, including detailed analysis of courtship signals. Herein, we analyzed, qualitatively and quantitatively, the reproductive behavior of Austrolebias reicherti. The behavioral units recognized in this study correspond with the previous analysis of other species of annual fishes. The most frequent unit in males was the lateral display where specific morphological and coloration patterns are displayed to the female. The female's high relative frequency and time of quietness suggest that this unit may have an evaluation role during courtship. In addition to visual displays during courtship, males perform vibrations of the dorsal and anal fins as well as body undulations; these indicate that mechanical signals may be important for attracting females. Our results support the hypothesis of multimodal signals. The conservation of behavioral patterns in courtship displays within Austrolebias suggests that species-level recognition and the barrier to hybridization may not occur at this stage, unless quantitative differences can be identified.

Os peixes anuais habitam charcos temporários que secam sazonalmente, e as adaptações para sobreviver a estas condições extremas incluem altas taxas metabólicas e um elaborado comportamento de cortejo, que culmina com a deposição de ovos resistentes à dessecação dentro do substrato, os quais são capazes de atravessar estádios de diapausa. O pronunciado dimorfismo sexual apresentado por estes peixes indica que a seleção sexual poderia estar exercendo um papel chave na diferenciação, especiação e evolução deste grupo diverso de peixes. Entretanto, informações acerca dos mecanismos de isolamento reprodutivo, incluindo uma análise detalhada dos sinais de cortejo, são escassas. Neste artigo é analisado o comportamento reprodutivo de Austrolebias reicherti de maneira qualitativa e quantitativa. As unidades comportamentais utilizadas neste estudo correspondem àquelas incluídas em análises anteriores de outras espécies de peixes anuais. A unidade comportamental mais freqüentemente observada em machos foi a "exibição lateral", onde características espécie-específicas da morfologia e colorido são exibidas para a fêmea. A alta proporção de ocorrência (em freqüência e tempo) do comportamento de "quietude" nas fêmeas indica que o mesmo poderia desempenhar um papel avaliativo durante o cortejo. Outros sinais além dos visuais estão envolvidos no cortejo dos peixes anuais; os machos vibram as nadadeiras dorsal e anal e ondulam o corpo, o que indica que os sinais mecânicos poderiam ter influência na atração das fêmeas. Estes resultados conferem suporte à hipótese de sinais multimodais, recentemente proposta. Os movimentos de cortejo altamente conservados dentro de Austrolebias indicam que o reconhecimento específico e a barreira à hibridização poderiam não ocorrer nesta etapa, a menos que se encontrem diferenças quantitativas nestes sinais comportamentais.