Critical thermal maxima in neotropical ants at colony, population, and community levels.

Global warming is exposing many organisms to severe thermal conditions and is having impacts at multiple levels of biological organisation, from individuals to species and beyond. Biotic and abiotic factors can influence organismal thermal tolerance, shaping responses to climate change. In eusocial ants, thermal tolerance can be measured at the colony level (among workers within colonies), the population level (among colonies within species), and the community level (among species). We analysed critical thermal maxima (CTmax) across these three levels for ants in a semiarid region of northeastern Brazil. We examined the individual and combined effects of phylogeny, body size (BS), and nesting microhabitat on community-level CTmax and the individual effects of BS on population- and colony-level CTmax. We sampled 1864 workers from 99 ant colonies across 47 species, for which we characterised CTmax, nesting microhabitat, BS, and phylogenetic history. Among species, CTmax ranged from 39.3 to 49.7°C, and community-level differences were best explained by phylogeny and BS. For more than half of the species, CTmax differed significantly among colonies in a way that was not explained by BS. Notably, there was almost as much variability in CTmax within colonies as within the entire community. Monomorphic and polymorphic species exhibited similar levels of CTmax variability within colonies, a pattern not always explained by BS. This vital intra- and inter-colony variability in thermal tolerance is likely allows tropical ant species to better cope with climate change. Our results underscore why ecological research must examine multiple levels of biological organisation.

Osteology of the Small-Sized Hyphessobrycon piabinhas Fowler 1941 (Characiformes, Characidae) With a Discussion on Developmentally Truncated Characters in the Family.

Evolutionary body size decrease has profound consequences for the morphology of an organism. In the evolution of the Characidae, the most species-rich family of Neotropical fishes, a prominent trend is the reduction of body size. The most typical effect is the simplification and reduction of morphological features through terminal deletion processes, resulting in the loss of skeletal elements and structures. To provide further information on the matter, we present a detailed description of the skeleton of Hyphessobrycon piabinhas, a poorly known, small representative of the largest genus of Characidae. We further discuss the identity and phylogenetic relationships of H. piabinhas. It belongs to the subfamily Stethaprioninae and exhibits considerable morphological similarity to other congeners from neighboring drainage systems. We identify several morphological simplifications in H. piabinhas and discuss them based on ontogenetic data available for Characiformes. These developmentally truncated elements are also present in many other small representatives of the family and seem to be among the first morphological modifications to occur in the context of body size reduction of Characidae. We argue that structural losses are not strictly correlated with sizes below 26 mm SL, although the most notable simplifications are typically observed in the miniatures.

Altitude is correlated with body size differences among Cotesia flavipes (Hymenoptera: Braconidae) wasps collected in two mountain ranges.

Living at high altitudes impose physiological and ecological challenges to which species may respond altering their body size, body proportions, and the shape of their body parts. Despite the importance of this topic for understanding the origin of species diversity, little attention has been invested in this phenomenon at the populational level. This paper study the relationship between altitude and body size, body proportions, and forewing shape venation of two populations of the parasitoid wasp Cotesia flavipes. Wasps were collected from Diatraea spp. larvae from sugarcane crops in two Colombian mountain ranges that cover between 600 m and 2143 m of altitude. Linear measurements of different body regions and geometric morphometrics of the forewing were subject to multivariate comparisons and allometric analyses to assess variation and to compare trends between ranges. Central (600 m to 1704 m) and Eastern Cordillera (877 m to 2143 m) populations showed different trends between body size and altitude. Allometric trends were not uniform within or between populations nor between structures. The allometric slopes of five body measurements from a single altitude differed from these from its own mountain range suggesting that body size trends along the cordilleras are a consequence of altitude and not of intrinsic body resource allocation processes. Wing shape between populations differed; however, these changes were poorly related to altitude. In agreement with recent studies in other groups, the observed allometric and wing shape differences between the two C. flavipes populations could be a plasticity response to altitude with interesting implications for posterior genetic differentiation.

Tracking anthropometric dimensions and grip strength among children, adolescents and adults in an indigenous community of southern Mexico: 1968-1978-2000.

PURPOSE: To track body size and proportions, arm dimensions and grip strength in children, adolescents, and adults resident in an indigenous community in Oaxaca who were measured on two or three occasions across surveys in 1968, 1978, and 2000. METHODS: The three cross-sectional surveys included measures of height, weight, sitting height, arm circumference, triceps skinfold, and grip strength in surveys of schoolchildren in 1968 and of schoolchildren, adolescents and adults in 1978 and 2000. Cross-checks of surnames, forenames and ages/dates of birth of participants in the three surveys identified three samples of individuals measured on two occasions (1968-1978, two age groups in 1978-2000) and a subsample of individuals measured in the three surveys. Partial correlations controlling for age at each observation were calculated for each variable in the three sex-specific samples measured on two occasions, and for the subsamples of males and females measured on three occasions. RESULTS: Allowing for variation in age among subsamples, inter-age correlations were moderate to high for stature, moderate for sitting height and estimated leg length, and low to moderate for weight, BMI, arm and estimated arm muscle circumference, triceps skinfold, and grip strength. CONCLUSION: Allowing for the relatively broad chronological age intervals, the inter-age correlations for height, weight and BMI were at the low end, while those for grip strength and for strength per unit body weight for males (though not females) were generally in the range of correlations noted in studies of European samples. Likely associated with improved health, nutritional, and sanitation conditions, obesity and overweight were emerging among adults by 2000. Obesity and overweight in adults paralleled the introduction of mechanized agriculture that reduced routine physical work. Among children, the association of obesity and overweight is likely with increased nutritional availability, but poor choices in diet.

Different approaches to understanding methodological adequacy in ecophysiological studies on small ectotherms.

Body temperature (Tb) variation and environmental temperature gradients are more intense in small individuals because their body size allows for a more intimate relationship between Tb and the environment. To contribute to a methodological consensus on the ecophysiology of small ectotherms, we aimed to investigate whether different approaches and methodological techniques affect the measurement of critical temperatures in a small lizard (Coleodactylus meridionalis, Sphaerodactylidae) from the Atlantic Forest of southern Bahia, Brazil, and subsequently its vulnerability assessment. We measured two metrics of thermal physiology: critical thermal minimum (CTmin) and critical thermal maximum (CTmax). In total, four types of temperature measurements (protocols) were defined. In the first protocol, we estimated CTmax/CTmin without heating/cooling rate by directly measuring the lizard's midbody temperature. In the other three protocols, we used a ramping assay with a heating/cooling rate to estimate CTmax/CTmin in the chamber (height: 11.3 cm), substrate, and Tb of the lizard, respectively. In total 116 individuals of Coleodactylus meridionalis were collected, of which 177 CTmax and 131 CTmin were performed. C. meridionalis showed a mean CTmax of 41 °C and a mean CTmin of 8.9 °C when considering the Tb protocol, which is intermediate compared to the other protocols. The substrate temperature protocol was the closest to Tb, and for this, the best method for the small lizards using an infrared thermometer.

Observed declines in body size have differential effects on survival and recruitment, but no effect on population growth in tropical birds.

Declines in body size can be an advantageous physiological response to warming temperatures, or a result of physiological and nutritional stress. Either way, studies often assume that these climate-induced trait changes have important implications for fitness and demography. We leveraged almost three decades of capture-mark-recapture data of 51 bird species in Panama to examine if body size has changed through time, how sensitive body size is to changes in weather, and if body size impacts population demography. We evaluated two metrics of body size, structural size (wing length), and body condition (residual body mass). Over the study, wing length changed in varying directions for 88% of species (23 decrease, 22 increase), but the effects were weak, and change was only significant for two species. Conversely, body condition declined for 88% of species (45), effects were stronger, and that change was significant for 22% of species (11). This suggests that nutritional stress is likely the cause of changes in body size, not an adaptive response to warming. Precipitation metrics impacted body condition across three of our four feeding guilds, while wing length was only impacted by weather metrics for two guilds. This suggests that body condition is more sensitive to change in weather metrics compared to wing length. Lastly, we found that the impact of changes in body size on survival and recruitment was variable across species, but these relationships were in the opposite direction, ultimately resulting in no change in population growth for all but one species. Thus, while different stages (adult survival and recruitment) of populations may be impacted by body size, populations appear to be buffered from changes. The lack of an effect on population growth rate suggests that populations may be more resilient to changes in body size, with implications for population persistence under expected climate change.

Critical swimming speed at different temperatures for small-bodied freshwater native riverine fish species.

This study evaluated the effect of fish total length (LT) and three water temperatures (10, 15 and 20 °C) on the critical swimming speed (Ucrit) of the species Percilia irwini (2.9-6.3 cm LT), Cheirodon galusdae (3.4-5.5 cm LT), and Trichomycterus areolatus (4.0-6.3 cm LT). An Ucrit estimation model was constructed for each species as a function of temperature and size. The results showed mean Ucrit for P. irwini of 44.56, 53.83 and 63.2 cm s-1 at 10, 15 and 20 °C, respectively: 55.34, 61.74 and 70.05 cm s-1 for C. galusdae and 56.18, 63.01 and 71.09 cm s-1 for T. areolatus. Critical velocity depended on the interaction between species, body length and water. The swimming performance increased significantly with rising temperature in all three species. The velocity also increased with greater fish total length. After controlling for fish total length, velocity also increased with higher temperature in the three species. This research is relevant to small fish species that require conservation measures.

Cross-habitat utilization of fish in a tropical deltaic system as a function of climate variability and body size: Are mangroves fish nurseries in a tropical delta?

The temporal variability of fish habitat utilization is poorly understood in tropical deltaic systems due to high water turbidity, which limits visual censuses, and to the lack of long-term data incorporating climate variability events. We aimed to assess the influence of body size and El Niño Southern Oscillation (ENSO) variability on the cross-habitat utilization rate of 14 fish species of commercial relevance in the Ciénaga Grande de Santa Marta (CGSM). We estimated the utilization of mangroves and coastal lagoons based on relative catch frequencies from encircling gillnets used within a long-term catch monitoring program, and then tested for significant changes in each species' habitat utilization as a function of body size and climate variability. Six species showed a high dependence on mangroves and four on coastal lagoons for most body size classes (including juveniles) and ENSO conditions. One species (Elops smithi) showed a high utilization of mangroves in some ENSO phases and body size classes, while three species showed a high utilization of both mangroves and coastal lagoons. Mangrove utilization by six species (Megalops atlanticus, E. smithi, Centropomus undecimalis, Mugil incilis, Mugil liza, and Ariopsis canteri) increased in larger body sizes at low depths, which usually occurs under dry ENSO conditions, when predatory risk is higher in coastal lagoons. Another species (Caquetaia kraussi) increased its mangrove utilization from the body size at which its feeding habits change. Mangroves and coastal lagoons are important nurseries and habitats for adults of the main commercial fish species in the CGSM. Seascape habitats and fringe/riverine mangroves must be conserved in tropical deltas to promote not only nurseries but also fish lifecycles.

Nest site correlates with nest type and body size in Troglodytidae passerines.

Nest characteristics are highly variable in the Passeriformes, but the macroevolutionary patterns observable for birds in general are not necessarily valid for specific families, suggesting that both global and within-family studies are needed. Here, we used phylogenetic comparative methods to address the evolutionary patterns of nest type, nest site and habitat in the Troglodytidae, a passerine group with diversified nest and habitat characteristics. The common ancestor of the Troglodytidae likely constructed enclosed nests within sheltered sites (cavity or crevice), but the radiation of the group was characterized by (i) shifts to exposed nest sites (vegetation) with retention of enclosed nests or (ii) retention of sheltered sites with nest simplification (cup nests). Nest site and nest type presented strong phylogenetic conservatism and evolved interdependently, while habitat was poorly correlated with nest evolution. A phylogenetic mixed modelling approach showed that sheltered nest sites were associated with small body size, likely to avoid competition with other animals for these places. With these results, we improve the understanding of nest character evolution in the Troglodytidae and reveal evolutionary aspects not observed so far for passerine birds.

Growth and allometric curves of southern brown howler monkey (Alouatta guariba): Insights on its ontogeny and conservation.

Ontogenetic sexual dimorphism is observed in different primate species, with ecological and evolutionary relationships explaining this pattern. Understanding the growth of the southern brown howler monkey elucidates not only the ecology and evolution but also contributes to conservation projects for this species. Throughout 20 years of the Centro de Pesquisas Biológicas de Indaial-Projeto Bugio, Brazil, we collected morphological data on 105 howlers of the Alouatta guariba species to identify the growth differences between ontogenetic categories and sexes and generate a growth curve to estimate the age of rescued individuals. Linear measurements were employed to obtain body length as well as the dimensions of the head and limbs. All individuals were also weighed to obtain body mass. We assessed growth rate and duration using allometric analysis based on the individuals' ages. We compared growth rate and duration among infant, juvenile, and adult howlers and between sexes. We provide growth curves for body size for both sexes using the Von Bertalanffy model. Infants have accelerated growth rate in comparison to the juveniles and adults, with no differences between sexes in establishing body length at this ontogenetic stage. Males have a prolonged development duration from the juvenile stage, reaching adulthood later than females, which explains the body length differences found in this species. Variables of head and limbs analyzed also showed differences in growth rate and duration, but not so consistently among ontogenetic stages. Mass was not a good variable to understand the growth differences of the animals, since many arrived feeble in the project and may have lost mass due to different circumstances in old age. Therefore, growth curves were obtained only for body length, allowing the estimation of the age of these animals when rescued from the wild to more effectively provide needed care in captivity.

Body Part Selection for Size Classification of Two Trichogramma Species.

Body size is an important morphological characteristic that covaries with the quality of parasitoids and predators. Data show that the larger the organism is, the better the biological parameters and the host location by natural enemies in the field. The standard way of evaluating the size of parasitoids of the genus Trichogramma (Hymenoptera: Trichogrammatidae) is by measuring the tibia, but using only one body part to estimate the size of organisms can lead to miscalculations. In this paper, commercial Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) and Trichogramma galloi Zucchi, 1988 (Hymenoptera: Trichogrammatidae) were mounted on slides for microscopy and photographed, and the photographs were used to measure their antennae, scutellum, ovipositor, tibia, and wing. Principal component analysis (PCA) and linear discriminant analysis (LDA) were performed to select the body part that best represents their size. PCA showed that all body parts represented size in a similar way, and LDA showed that the ovipositor was the most representative. We conclude that the best body parts for representing the size of the Trichogramma species studied are the wing and ovipositor, and at least two body parts are needed to detect two size groups.

Life-history of the spiny butterfly ray, Gymnura altavela (Chondrichthyes: Myliobatiformes), kept under human care in a marine aquarium.

The Rio de Janeiro Marine Aquarium (AquaRio) is the first to successfully maintain and reproduce the spiny butterfly ray (Gymnura altavela), providing unique information about the species' biology. Seven rays were kept in captivity between 2018 and 2023, two captured on the southeastern coast of Brazil and five born in the aquarium. The applied abiotic conditions and nutrition allowed for the survival, growth, and reproduction of these individuals. Growth parameters (asymptotic disk width-DW∞ and growth coefficient-k) were estimated based on the von Bertalanffy model using the Fabens method for males and females separately. The best models estimated DW∞ = 106.47 cm and k = 0.396 for males and DW∞ = 172.2 cm and k = 0.190 for females. Sexual dimorphism was corroborated, with females reaching larger sizes and presenting slower growth rates than males. The estimated k values were higher than those estimated for rays of similar size to G. altavela in the natural environment, probably due to the constant water temperature (around 25.5°C), food abundance, low population density, reduced predation rates, and high water quality in the captive environment. A comparison of the captivity findings with other studies on G. altavela age and growth in the Atlantic and Mediterranean indicates a broad phenotypic plasticity regarding growth. Three G. altavela reproductions were recorded, with size at birth appearing to be a key factor for pup's survival. Behavioral pattern observations associated with reproduction are also described, encompassing chasing and copulation, whereas the species' internal morphology is described through coelomic cavity ultrasound scanning.

A phylogeny-informed characterisation of global tetrapod traits addresses data gaps and biases.

Tetrapods (amphibians, reptiles, birds, and mammals) are model systems for global biodiversity science, but continuing data gaps, limited data standardisation, and ongoing flux in taxonomic nomenclature constrain integrative research on this group and potentially cause biased inference. We combined and harmonised taxonomic, spatial, phylogenetic, and attribute data with phylogeny-based multiple imputation to provide a comprehensive data resource (TetrapodTraits 1.0.0) that includes values, predictions, and sources for body size, activity time, micro- and macrohabitat, ecosystem, threat status, biogeography, insularity, environmental preferences, and human influence, for all 33,281 tetrapod species covered in recent fully sampled phylogenies. We assess gaps and biases across taxa and space, finding that shared data missing in attribute values increased with taxon-level completeness and richness across clades. Prediction of missing attribute values using multiple imputation revealed substantial changes in estimated macroecological patterns. These results highlight biases incurred by nonrandom missingness and strategies to best address them. While there is an obvious need for further data collection and updates, our phylogeny-informed database of tetrapod traits can support a more comprehensive representation of tetrapod species and their attributes in ecology, evolution, and conservation research.

Giant stem tetrapod was apex predator in Gondwanan late Palaeozoic ice age.

Current hypotheses of early tetrapod evolution posit close ecological and biogeographic ties to the extensive coal-producing wetlands of the Carboniferous palaeoequator with rapid replacement of archaic tetrapod groups by relatives of modern amniotes and lissamphibians in the late Carboniferous (about 307 million years ago). These hypotheses draw on a tetrapod fossil record that is almost entirely restricted to palaeoequatorial Pangea (Laurussia)1,2. Here we describe a new giant stem tetrapod, Gaiasia jennyae, from high-palaeolatitude (about 55° S) early Permian-aged (about 280 million years ago) deposits in Namibia that challenges this scenario. Gaiasia is represented by several large, semi-articulated skeletons characterized by a weakly ossified skull with a loosely articulated palate dominated by a broad diamond-shaped parasphenoid, a posteriorly projecting occiput, and enlarged, interlocking dentary and coronoid fangs. Phylogenetic analysis resolves Gaiasia within the tetrapod stem group as the sister taxon of the Carboniferous Colosteidae from Euramerica. Gaiasia is larger than all previously described digited stem tetrapods and provides evidence that continental tetrapods were well established in the cold-temperate latitudes of Gondwana during the final phases of the Carboniferous-Permian deglaciation. This points to a more global distribution of continental tetrapods during the Carboniferous-Permian transition and indicates that previous hypotheses of global tetrapod faunal turnover and dispersal at this time2,3 must be reconsidered.

Characterization of a Peruvian coastal fishery targeting the Pacific guitarfish Pseudobatos planiceps.

From December 2012 to June 2014, 796 Pacific guitarfish were caught in 183 fishing sets in northern Peru. Catch occurred in 86.3% of sets. Most individuals caught were mature with a bias toward males. The mean total length for females and males was 83.4 cm, and 91.1 cm, respectively. The capture per unit effort (CPUE) was 12.6 ± 3.4 guitarfish (km.12 h)-1. The length-weight relationships showed that this species presents a sexual dimorphism in growth. These results support the importance of Sechura Bay as a key area for this species. This study represents the first species-specific fishery data for the Pacific guitarfish.

Feeding protocol with live feed and inert diet to determine the ideal age/size for weaning mullet Mugil liza (Valenciennes, 1836).

The Lebranche mullet Mugil liza is a marine fish of great importance for artisanal and industrial fishing, as well as aquaculture. The use of live feeds during the larviculture phase of marine fish is a significant component of production costs. The present study evaluated the effects of the feeding transition on different larval stages of M. liza, from the combined supply of live feed (Brachionus rotundiformis + Artemia franciscana) and live + inert feed (Artemia franciscana + inert diet) until the weaning phase to only the inert diet. A total of 3240 M. liza larvae (weight 0.0133 ± 0.0062 g and length 0.793 ± 0.160 cm) were distributed among the 12 experimental units (n = 270), resulting in four groups with three replicates each. Treatment groups consisted of feed transition with A. franciscana (enriched metanauplii) to commercial inert feed starting weaning at four different larval ages: 28, 31, 34, and 37 days post hatching. Zootechnical performance indexes and intestinal histomorphometry were evaluated. Mortality, condition factor, and length variation coefficient did not show significant differences between treatments. Final weight, final length, weight gain, and length gain were significantly greater in larvae that started weaning at 31, 34, and 37 days post hatching. Weight coefficient of variation was significantly higher in larvae that started weaning at 28 days (67.51 ± 11.70) compared to 37 days (34.40 ± 7.30). In intestinal histology, villi height (180.3 ± 4.4) was significantly higher in larvae that started weaning at 37 days post hatching. Considering the evidence found in the present study, it is recommended to start weaning M. liza on the 31st day post-hatching, using a 2-day co-feeding protocol (31st and 32nd days). From the 33rd day after hatching, M. liza larvae can receive only commercial feed.

Discrimination of cryptic species: Tabanus triangulum and Tabanus occidentalis (Diptera: Tabanidae) differ in size and shape.

Horse fly females (Diptera, Tabanidae) are hematophagous and can vector pathogens that affect livestock. Complexes of cryptic species are common in Tabanidae, as exemplified by some species of Tabanus, including Tabanus triangulum and Tabanus occidentalis, both prevalent in the Southern region of Brazil. In this study, geometric morphometrics were employed to ascertain the wing venation in species identification. It was demonstrated that this tool effectively differentiates T. triangulum from T. occidentalis in the coastal plain of Rio Grande do Sul state, situated within the Pampa biome. The results indicate that T. triangulum and T. occidentalis occupy distinct regions of the morphological space, allowing their precise identification through geometric morphometrics, which is fast, affordable, and easy to implement.

Does the body size, sex, and reproductive modes of leaf litter anurans affect the diversity of parasites?

We describe the composition of endoparasites associated with leaf litter anurans from an Atlantic Forest area, in southeastern Brazil. We tested if body size, sex, and reproductive modes of anuran hosts influence endoparasite abundance and richness. We sampled 583 individuals from 11 anuran species and recorded 1,600 helminths from 14 taxa. The helminths that infected the greatest number of anuran host species were the nematodes Cosmocerca parva (8 spp.), Physaloptera sp. (8 spp.), and Cosmocerca brasiliense (7 spp.), and the most abundant helminth species were Physaloptera sp. (14.6%), Cosmocerca brasiliense (13.7%) and Cosmocerca parva (12.6%). Both helminth abundance and richness were positively affected by anuran body size and dependence on water for reproduction. Larger hosts can contain a higher abundance of parasites because they may provide more physical space than smaller ones, or it can simply be a function of age. Besides, parasite species richness can be highly correlated with the amount of time a host spends in association with aquatic habitats, a conservative aspect of both parasite and host natural history. Within host species, there was a positive and significant influence of body size on helminth abundance. Haddadus binotatus females had greater helminth abundance than males, probably due to sex-related differences in behavior and/or in physiology. Our data suggest that reproductive modes could also influence helminth infection parameters in other anuran communities and should be considered in detail in future analyses.

Body size predicts ontogenetic nitrogen stable-isotope (δ15N) variation, but has little relationship with trophic level in ectotherm vertebrate predators.

Large predators have disproportionate effects on their underlying food webs. Thus, appropriately assigning trophic positions has important conservation implications both for the predators themselves and for their prey. Large-bodied predators are often referred to as apex predators, implying that they are many trophic levels above primary producers. However, theoretical considerations predict both higher and lower trophic position with increasing body size. Nitrogen stable isotope values (δ15N) are increasingly replacing stomach contents or behavioral observations to assess trophic position and it is often assumed that ontogenetic dietary shifts result in higher trophic positions. Intraspecific studies based on δ15N values found a positive relationship between size and inferred trophic position. Here, we use datasets of predatory vertebrate ectotherms (crocodilians, turtles, lizards and fishes) to show that, although there are positive intraspecific relationships between size and δ15N values, relationships between stomach-content-based trophic level (TPdiet) and size are undetectable or negative. As there is usually no single value for 15N trophic discrimination factor (TDF) applicable to a predator species or its prey, estimates of trophic position based on δ15N in ectotherm vertebrates with large size ranges, may be inaccurate and biased. We urge a reconsideration of the sole use of δ15N values to assess trophic position and encourage the combined use of isotopes and stomach contents to assess diet and trophic level.

New insights into the reproduction and migration of the porbeagle shark Lamna nasus (Bonnaterre 1788) in the Southwest Atlantic Ocean.

The objective of this study was to estimate the reproductive parameters of porbeagle shark in the Southwest Atlantic Ocean and thus characterize the adult fraction of this population. Therefore, 1012 specimens were measured by scientific observers on board the commercial trawl fleet operating south of 50° S. The size range of the specimens was from 77 to 292 cm fork length (LF). The mean size at maturity was estimated to be 153 cm LF for males and 172 cm LF for females. Porbeagle shark catches were recorded throughout the year, with the highest frequency occurring between November and June. The presence of pregnant females was observed from December to July, along with an increase in the average size of embryos in each litter. The information presented in this study improves the knowledge of the reproductive biology and allows to propose a migratory pattern of adult porbeagle females in the Southwest Atlantic Ocean. The likely seasonal increase in vulnerability of this shark to austral trawl fishery, despite all conservation management measures established in Argentina, underscores the importance of promoting its proper management and conservation given the need to improve understanding of porbeagle population dynamics in the Southern Hemisphere.