The size of signal detection and emission organs in a synchronous firefly: sexual dimorphism, allometry and assortative mating.

The size of the organs responsible for emitting and detecting sexual communication signals is a likely target for selection. Communication via bioluminescent signals in synchronous fireflies is a promising model to test hypotheses regarding differences between males and females in the effect of the size of signal emission and detection organs on fitness components. Synchronous firefly species congregate in large numbers during the mating season, displaying bioluminescent signals aimed at potential mates during relatively short nightly periods. Operational sex ratios are male-biased and, thus, the so-called typical sex roles (indiscriminate males and choosy females) are expected to evolve. We studied the synchronous firefly Photinus palaciosi, a species that during the mating season congregates in forests of central Mexico offering a magnificent natural show that attracts numerous tourists. P. palaciosi females have reduced wings (brachyptery) and cannot fly. Our field study tested the hypothesis that the male-biased operational sex ratio and the short daily mating period result in strong male-male competition that selects for males with larger lanterns and larger eyes, and against male mate choice, whereas female-female mate competition is absent and, thus, no selection on lantern or eye size is expected. Even though lantern, eye or body size do not predict the probability of being found in copula for either sex, sexual dimorphism in these features, along with allometric slopes of lantern size and assortative mating in terms of relative lantern size, support not only the hypothesis of intense sexual selection among males, but the possibility of subtle mechanisms of sexual selection among females. Trade-offs between investment in signaling (lanterns) versus detection (eyes) structures, or with pressures different from sexual selection such as those imposed by predators, are also likely to be important in shaping the evolution of sexual signaling in these fireflies.

Sex-related interannual plasticity in wing morphological design in Heliconius charithonia enhances flight metabolic performance.

Flight morphological variations and its consequences on animal performance are common in winged insects. In the butterfly Heliconius charithonia, sex-related differences in the wing morphological design have been described resulting in differences in foraging behavior, daily flight distances and flight aerodynamics. It has been suggested that these differences should be reflected in the metabolic capacities and energetic budgets associated with flight in both sexes. In this study, we analyzed the relationship between wing morphological variation and metabolic performance, flight aerodynamics and energetic reserves in females and males of Heliconius charithonia over two years. The results confirm the presence of wing shape sexual dimorphism, but also show an unexpected sex-related annual variation in wing shape, mirrored in the metabolic condition (resting metabolic rate) of individuals. However, contrary to expectation, intersexual variations in wing shape are not related to differences between the sexes in terms of flight aerodynamics, flight metabolic rates, or energetic reserves (carbohydrates, lipids and proteins). Our results indicate a considerable plasticity in H. charithonia wing shape, which we suggest is determined by a trade-off between environmental pressures and reproductive restriction of each sex, maintaining an optimum flight design. Finally, similarities in metabolic rates between young and older males and females in both years may be a consequence of the ability of Heliconius species to feed on pollen.

Spatial aggregation of fruits explains food selection in a neotropical primate (Alouatta pigra).

The availability and spatial distribution of food resources affect animal behavior and survival. Black howler monkeys (Alouatta pigra) have a foraging strategy to balance their nutrient intake that involves mixing their consumption of leaves and fruits. The spatial aggregation of food items should impact this strategy, but how it does so is largely unknown. We quantified how leaf and fruit intake combined (here termed food set selection) was spatially aggregated in patches and how food aggregation varied across seasons. Using variograms we estimated patch diameter and with Generalized Least Square models determined the effect of food spatial aggregation on food selection. Only fruits were structured in patches in the season of highest availability (dry-season). The patches of food set selection had a diameter between 6.9 and 14 m and were explained by those of mature fruit availability which were between 18 and 19 m in diameter. Our results suggest that the spatial pattern of food selection is influenced by patches of large fruit-bearing trees, not by particular species. Fruit also occur along spatial gradients, but these do not explain food selection, suggesting that howlers maximize food intake in response to local aggregation of fruit that are limiting during certain seasons. We demonstrate how the independent spatial modelling of resources and behavior enables the definition of patches and testing their spatial relationship.

Males, but not females, perform strategic mate searching movements between host plants in a leaf beetle with scramble competition polygyny.

Mate searching is assumed to be performed mostly by males, but when females benefit from multiple mating or are under risk of failing to mate, they may also perform mate searching. This is especially important in scramble competition polygynies, in which mate searching is the main mechanism of mate competition. Typically, more mobile individuals are expected to achieve higher mating success because mobility increases their probability of finding mates. If we assume individual movements are mainly explained by mate searching in scramble competition polygynies, we can investigate searching strategies by asking when individuals should leave their location and where they should go. We hypothesize that individuals will leave their locations when mating opportunities are scarce and will seek spatially close sites with better mating opportunities. We tested these hypotheses for males and females of Leptinotarsa undecimlineata, a leaf beetle with scramble competition polygyny in which both sexes are promiscuous. Individuals mate and feed exclusively on Solanum plants, and thus, individual movements can be described as switches between plants. Females were less likely than males to leave isolated plants, and both males and females moved preferentially to neighboring plants. Males were more likely to leave when the local number of females was low, and the number of males was high. They moved to plants with more females, a behavior consistent with a mate searching strategy. Females were more likely to move to plants with fewer males and many females, a behavior consistent with male harassment avoidance. Strategic movement is widely considered in foraging context, but seldom in a mate searching context. Considering that selection to minimize searching costs, maximize mating success, and minimize harassment may be ubiquitous in nature, we argue that strategic movements by mate searching individuals are likely to occur in many species.

Contests over reproductive resources in female roller beetles: Outcome predictors and sharing as an option.

Fights among females are frequent, although less attention has been placed on them than on male fights. They arise when females compete for food, oviposition, mates, brooding sites, or access to resources which increase offspring survival. It has been shown that the outcome of female fights may be less predictable by asymmetries in resource holding power, than in male fights. Male roller beetles fight over food resources, food balls, needed for mating and nesting, and it has been show in some species that asymmetries in reproductive experience and resource holding power in terms of size predict fight outcome, including ties in which contenders cut and split the food ball. In this study, we tested the influence of asymmetries in reproductive status (experience) and body size on female fight outcome in the carrion roller beetle Canthon cyanellus cyanellus. As predicted, and as previously found for males of the same species, female reproductive status of both contenders and relative size predict fight outcome. Larger and reproductively experienced contenders have a higher probability of winning. Furthermore, ties are more likely in fights involving opposing asymmetries (vgr. Large reproductively naïve owner versus small reproductively experienced intruder). Also as predicted, food ball splitting is more likely to be started by the predicted loser. This mode of resource sharing may be the result of a fighting strategy in which the costs of continuing to fight are greater than the benefits of not splitting, if a fraction of the disputed resource is more than the minimum needed for the present reproductive needs, and reduces costs associated to a longer fight.

Macroecology of Sexual Selection: A Predictive Conceptual Framework for Large-Scale Variation in Reproductive Traits.

Abiotic factors exert direct and indirect influences on behavioral, morphological, and life-history traits. Because some of these traits are related to reproduction, there is a causal link between climatic conditions and the expression of reproductive traits. This link allows us to generate predictions on how reproductive traits vary in large geographic scales. Here we formalize this macroecological framework, present some general predictions, and explore empirical examples using harvestmen as study organisms. Our results show that the length of breeding season in harvestmen is primarily influenced by the number of warm months and that precipitation plays a secondary role in modulating the period devoted to reproduction. Moreover, we show that the probability of resource defense polygyny increases with longer breeding seasons and that the presence of this type of mating system positively affects the magnitude of sexual dimorphism in harvestmen. Finally, the presence of postovipositional parental care is also influenced by the length of breeding season but not by actual evapotranspiration, which is our proxy for the intensity of biotic interactions. We argue that the macroecological framework proposed here may be a fruitful field of investigation, with important implications for our understanding of sexual selection and the evolution of reproductive traits in both animals and plants.

Phenology of scramble polygyny in a wild population of chrysomelid beetles: the opportunity for and the strength of sexual selection [corrected].

Recent debate has highlighted the importance of estimating both the strength of sexual selection on phenotypic traits, and the opportunity for sexual selection. We describe seasonal fluctuations in mating dynamics of Leptinotarsa undecimlineata (Coleoptera: Chrysomelidae). We compared several estimates of the opportunity for, and the strength of, sexual selection and male precopulatory competition over the reproductive season. First, using a null model, we suggest that the ratio between observed values of the opportunity for sexual selections and their expected value under random mating results in unbiased estimates of the actual nonrandom mating behavior of the population. Second, we found that estimates for the whole reproductive season often misrepresent the actual value at any given time period. Third, mating differentials on male size and mobility, frequency of male fighting and three estimates of the opportunity for sexual selection provide contrasting but complementary information. More intense sexual selection associated to male mobility, but not to male size, was observed in periods with high opportunity for sexual selection and high frequency of male fights. Fourth, based on parameters of spatial and temporal aggregation of female receptivity, we describe the mating system of L. undecimlineata as a scramble mating polygyny in which the opportunity for sexual selection varies widely throughout the season, but the strength of sexual selection on male size remains fairly weak, while male mobility inversely covaries with mating success. We suggest that different estimates for the opportunity for, and intensity of, sexual selection should be applied in order to discriminate how different behavioral and demographic factors shape the reproductive dynamic of populations.

Molecular systematics of sclerosomatid harvestmen (Opiliones, Phalangioidea, Sclerosomatidae): geography is better than taxonomy in predicting phylogeny.

Phylogenetic relationships within the Sclerosomatidae, the largest family of harvestmen, are explored using molecular data from four nuclear genes (28S and 18S rRNA, Histone 3 and Elongation factor-1α) and two mitochondrial gene regions (COI-COII, 16S and 12S rRNA). The taxon sample includes representative species from all families in Phalangioidea and all subfamilies of Sclerosomatidae (Gagrellinae, Gyinae, Leiobuninae, Sclerosomatinae). Our results solve several major taxonomic problems, including placement of Gyinae sensu stricto in Phalangiidae, the monophyly of the Metopilio group and its exclusion from Sclerosomatidae, and reaffirmation of the familial rank of Protolophidae. However, most major groups of sclerosomatids (Leiobuninae, Gagrellinae, Leiobunum, Nelima) are recovered as polyphyletic, although with a phylogenetic structure suggesting a strong association between geography and monophyly as well as notable morphological convergence in traditional diagnostic characters. Phylogenetic affinities between biotas of the New World and Asian tropics, as well as between temperate North American and East Asia, suggest that sclerosomatid historical biogeography may conform with the Boreotropic Concept. Finally, we discuss how the many problems that remain in sclerosomatid systematics might be addressed.

Sexually dimorphic legs in a neotropical harvestman (Arachnida, Opiliones): ornament or weapon?

The evolution of sexually dimorphic traits has been the focus of much theoretical work, but empirical approaches to this topic have not been equally prolific. Males of the neotropical family Gonyleptidae usually present a strong fourth pair of legs armed with spines, but their functional significance is unknown. We investigated the putative functions of the leg armature in the harvestman Neosadocus maximus. Being a non-visual species, the spines on male legs can only be perceived by females through physical contact. Thus, we could expect females to touch the armature on the legs of their mates if they were to evaluate it. However, we found no support for this hypothesis. We did show that (1) leg armature is used as a weapon in contests between males and (2) spines and associated sensilla are sexually dimorphic structures involved in "nipping behavior", during which a winner emerged in most fights. Finally, we demonstrate that five body structures directly involved in male-male fights show positive allometry in males, presenting slopes higher than 1, whereas the same structures show either no or negative allometry in the case of females. In conclusion, leg armature in male harvestmen is clearly used as a device in intrasexual contests.

Analysing body condition: mass, volume or density?

1. Body condition (defined as the relative amount of energy reserves in the body) is an animal trait with strong ecological implications. In some animal taxa (e.g. arthropods), the external volume of the body part in which most nutrients are stored (e.g. abdomen) is used interchangeably with body mass to estimate body condition, making the implicit assumption that abdomen residual volume is a good surrogate of residual mass. However, the degree of correlation between these two measures should largely depend on the density of the nutrients stored. 2. We simulated two food-supplemented experimental groups of animals, each storing a slightly different amount of lipids either in their abdomens or in their entire bodies, and explored (i) how different estimates of condition were able to detect fixed differences between the groups; and (ii) how the amount of lipids stored could affect the outcome of non-intrusive measures of condition on a dichotomous variable (e.g. survival, mating success). We found that density body condition (body mass statistically controlled for structural body size and body volume) has much greater power to detect differences between experimental groups or effects on binary response variables than do classic mass/size or volume/size condition indices. 3. Using data on Lycosa tarantula (L.), a burrowing wolf spider, we report dramatic differences among these three indices in their ability to detect sex differences in the effect of feeding treatment on body condition at maturity. In particular, a plot of residual mass against residual volume reflecting nutrient density suggests that poorly fed spiders are nutritionally unbalanced, since well-fed spiders invest in nutrients of very different density. 4. Furthermore, using data on Scathophaga stercoraria (L.), the yellow dung fly, we found that an index of density condition was better at distinguishing condition differences among three populations than were mass or volume condition estimates alone. 5. We propose that including these three surrogates of condition (mass, volume and density) will substantially improve the accuracy of non-intrusive estimates of body condition, thus providing more powerful tools with direct application in a wide range of disciplines.

Nonhost status of Citrus sinensis cultivar valencia and C. paradisi cultivar ruby red to Mexican Anastrepha fraterculus (Diptera: Tephritidae).

Anastrepha fraterculus (Wiedemann) is recognized as a pest of citrus, apples, and blackberries in South America. In Mexico, it is mainly found in fruit of the family Myrtaceae and has never been reported infesting citrus. Here, we sought to determine whether females stemming from Mexican A. fraterculus populations (collected in the state of Veracruz) would lay eggs in 'Valencia' oranges and 'Ruby Red' grapefruit and, if so, whether larvae would hatch and develop. We worked under laboratory and seminatural conditions (i.e., gravid females released in fruit-bearing, bagged branches in a commercial citrus grove) and used Anastrepha ludens (Loew), a notorious pest of citrus, as a control species. Under laboratory conditions, A. ludens readily accepted both oranges and grapefruit as oviposition substrates, but A. fraterculus rarely oviposited in these fruit (but did so in guavas, a preferred host) and no larvae ever developed. Eggs were deposited in the toxic flavedo (A. fraterculus) and nontoxic albedo (A. ludens) regions. Field studies revealed that, as was the case in the laboratory, A. fraterculus rarely oviposited into oranges or grapefruit and that, when such was the case, either no larvae developed (oranges) or of the few (13) that developed and pupated (grapefruit), only two adults emerged that survived 1 and 3 d, respectively (5-17% of the time necessary to reach sexual maturity). In sharp contrast, grapefruit exposed to A. ludens yielded up to 937 pupae and adults survived for >6 mo. Therefore, the inability of Mexican A. fraterculus to successfully develop in citrus renders the status of Mexican A. fraterculus as a pest of citrus in Mexico as unsubstantiated.