Sexual Dimorphism In Body Size Research Articles

Lethal Aggression in Captive Monkeys

Establishing the characteristics of monkey lethal aggression, assessing the age and sex of aggressors and victims, and the nature of the aggressors' actions seems necessary to identify the evolutionary roots of cases of human lethal aggression. In addition, the study of the features of lethal aggression can be considered as a condition for the development of measures aimed at preventing its manifestations in captive monkeys. The aim of the study is to study the species-specific features of lethal aggression in captive macaques, baboons and guenons. An analysis was made of cases of intra-group lethal aggression that occurred over a 10-year period in Rhesus macaques (Macaca mulatta), Crab-eathing macaques (Macaca fascicularis), Pig-tail macaques (Macaca nemestrina), Green monkeys (Chlorocebus aethiops), Hamadryas baboons (Papio hamadryas), Anubis baboons (Papio anubis) kept by social groups. It has been established that cases of lethal aggression are observed in all 6 studied species of monkeys. It was shown that in groups consisting of adult males, the highest frequency of cases of lethal aggression was noted in Rhesus macaques, and the lowest in Hamadryas baboons. Species-specific differences were found in the nature of lethal aggression in monkey family groups consisting of males, females, infants, and adolescents. It has been established that in Hamadryas baboons, Anubis baboons and Pig-tail macaques, that is, in species with pronounced sexual dimorphism in body size and social status, the main form of lethal aggression in family groups is infanticide committed by a single sexually mature male. In Rhesus monkeys, Crab-eathing macaques and Green monkeys, that is, those species that are characterized by relatively mild sexual dimorphism in body size and social status, the predominant form of lethal aggression in family groups is the collective actions of females aimed at young and adult members of the group.

Sexual dimorphism in body size and some exterior traits of pigeon breed groups

In this study, sexual dimorphism in pigeons was investigated. Rensch's rule was evaluated across pigeon breeds. Body weight, body length, beak length, wingspan, tail length, and tarsus length were used for the analysis. We have divided the breeds in the five groups (form, frills and owls, tumbler and rollers, homer and highflyer, feral). The allometric relation in the traits between female and male measures were analyzed. The measure of sexual size dimorphism was measured for each trait as a simple male size divided by female size (Sexual Size Index, SSI). On average across traits, male birds have higher values than female birds, both across breed groups and overall. No deviation from isometric allometry can be observed except the tail length. No trends towards logarithmic female values according to the SSI could be identified. According to the results, the rules of Rensch for pigeon breeds are rejected. Sexual dimorphism exists between breeds and traits, mainly in favor of the male birds. In most cases, allometric relationships between breeds change, as do traits.

Sex-specific responses to growth hormone and luteinizing hormone in a model teleost, the Mozambique tilapia

Across the vertebrate lineage, sexual dimorphism in body size is a common phenomenon that results from trade-offs between growth and reproduction. To address how key hormones that regulate growth and reproduction interact in teleost fishes, we studied Mozambique tilapia (Oreochromis mossambicus) to determine whether the activities of luteinizing hormone (Lh) are modulated by growth hormone (Gh), and conversely, whether targets of Gh are affected by the presence of Lh. In particular, we examined how gonadal morphology and specific gene transcripts responded to ovine GH (oGH) and/or LH (oLH) in hypophysectomized male and female tilapia. Hypophysectomized females exhibited a diminished gonadosomatic index (GSI) concomitant with ovarian follicular atresia. The combination of oGH and oLH restored GSI and ovarian morphology to conditions observed in sham-operated controls. A similar pattern was observed for GSI in males. In control fish, gonadal gh receptor (ghr2) and estrogen receptor β (erβ) expression was higher in females versus males. A combination of oGH and oLH restored erβ and arβ in females. In males, testicular insulin-like growth factor 3 (igf3) expression was reduced following hypophysectomy and subsequently restored to control levels by either oGH or oLH. By contrast, the combination of both hormones was required to recover ovarian igf3 expression in females. In muscle, ghr2 expression was more responsive to oGH in males versus females. In the liver of hypophysectomized males, igf2 expression was diminished by both oGH and oLH; there was no effect of hypophysectomy, oGH, or oLH on igf2 expression in females. Collectively, our results indicate that gene transcripts associated with growth and reproduction exhibit sex-specific responses to oGH and oLH. These responses reflect, at least in part, how hormones mediate trade-offs between growth and reproduction, and thus sexual dimorphism, in teleost fishes.

Echolocation repetition rate as a proxy to monitor population structure and dynamics of sperm whales

AbstractCharacterizing population structure and dynamics is critical for the conservation of endangered species. Monitoring sperm whales Physeter macrocephalus is especially difficult because it requires monitoring different latitudes to capture the dynamics of most populations. Since their remarkable sexual dimorphism in body size is reflected in their sounds, passive acoustic monitoring presents an opportunity to capture contiguous patterns in time, space, and over large scales. We show that the echolocation repetition rate (measured as inter‐click interval, ICI) as a proxy for body length is a suitable approach for large‐scale acoustic monitoring. Body length has previously been estimated from the time interval between pulses (IPI) within sperm whale echolocation clicks. These estimates can only be achieved when whales are oriented toward the recorder or directly facing away, resulting in sparse data. A representative subsample of data demonstrated that ICI and IPI are linearly correlated, allowing conversion of ICI distributions into likely body length categories. This approach was applied to three monitoring sites in the Gulf of Mexico (2010–2017), where sperm whale population structure and male movements were poorly understood. We identified three classes: large animals between 12–15 m (ICI between 0.72 and 1 sec), presumed to correspond to adult males, and small animals below 12 m (ICI between 0.44 and 0.64 sec) likely pertaining to social groups (mixed groups with adult females and their offspring), and the third class with mid‐sized animals (ICI between 0.64 and 0.83 sec) believed to contain adult females or sub‐adult males. Our results revealed spatial and seasonal variability of the population structure including possible male presence throughout the year and migratory patterns of the population. This approach provides a means to efficiently characterize the putative population structure of sperm whales to understand the population's geographical dynamics and population status, which is relevant under rapidly changing habitat conditions.

Sexually Dimorphic Responses to Growth Hormone and Luteinizing Hormone within the Somatotropic and Reproductive Axes of Tilapia

Sexual dimorphism in body size is a common phenomenon among vertebrates, including teleost fishes. The hormonal underpinnings of this phenomenon, however, have not been fully clarified and may be associated with interactions between the endocrine factors that control growth and reproduction. Given their well‐described patterns of sexually dimorphic growth, we used Mozambique tilapia (Oreochromis mossambicus) as a model to examine how the activities of luteinizing hormone (LH) are modulated by growth hormone (GH), and conversely, how LH affects targets of GH. We hypothesized that GH would induce factors within the GH/insulin‐like growth factor (GH/IGF) axis that favor growth, while LH would attenuate growth‐promoting factors and stimulate factors that favor reproduction. We analyzed gonad morphology and gene expression in hypophysectomized tilapia injected with ovine GH (oGH) and LH (oLH) either alone or in combination. Gonadosomatic index (GSI) was reduced in females following hypophysectomy; the combined administration of oGH and oLH restored GSI to control levels. Hypophysectomy regressed the ovary and the combined treatment of oGH and oLH restored ovarian structure. Gonadal gh receptor (ghr2) and estrogen receptor β (erβ) were higher in females, whereas igf1, igf3, erα, and androgen receptor ß (arß) were higher in males of control fish. The inhibitory effects of hypophysectomy were most pronounced on igf3transcripts, and these levels were restored by both oGH and oLH alone, or in combination, in males. In females, the combination of both hormones was required to recover gonadal igf3 levels. A hypophysectomy‐induced decrease in arβ was restored by a combination of oGH and oLH in females, while there were no effects of oGH or oLH on arβ in males. In muscle, ghr2 was more responsive to oGH in males, while igf2 was more responsive to oLH in females. oGH and oLH both inhibited a hypophysectomy‐induced increase in hepatic igf2 in males. Our results indicate that genes associated with growth and reproduction exhibit sexually dimorphic responses to GH and LH in tilapia, and therefore, provide insight into the endocrine bases of sexually dimorphic growth in fishes.

Sexual Dimorphism in Body Size and Wing Loading for Three Cicada Species

Abstract Sexual dimorphism in body size has been observed for many insect species. However, whether dimorphism influences the flight performance for closely related insects or between the genders of conspecifics has seldom been examined. Wing loading (i.e., body mass/total wing area, WL = M/A) is an important indicator of flight efficiency and maneuverability. We examined the potential for sexual dimorphism and interspecific differences in wing loading for three cicada species (Cryptotympana atrata, Meimuna mongolica, and Platypleura kaempferi) and tested the hypothesis that females have higher WLs than males possibly because they must carry the extra weight of eggs. There were significant dimorphic differences in body mass and WL for each of the three species. However, there were no significant dimorphic differences in total wing area for C. atrata and M. mongolica, whereas P. kaempferi females had larger mean total wing area than males. Among the three cicada species, males had lower WLs (and by inference, greater maneuverability) than females. In addition, the M vs. A scaling exponent (i.e., α) was numerically significantly greater than unity (i.e., α > 1). Thus, WL should scale with respect to M with α > 1, which accounts for why females have a larger WL than males. We interpret these results to indicate that gender dimorphism in body size and flight performance likely reflect selection on traits affecting reproductive success that, in turn, likely depend on flight maneuverability.

Monogamy in the Burrowing Shrimp Axianassa australis Rodrigues & Shimizu, 1992 (Decapoda, Gebiidea, Axianassidae).

Our knowledge of the mating systems in burrowing shrimps (infraorders Axiidea and Gebiidea) is still rather limited. Here we describe the burrow use pattern, sex ratio, and sexual dimorphism of the burrowing shrimp Axianassa australis to test for monogamy, considering that monogamous species live in heterosexual pairs and exhibit a low degree of sexual dimorphism. To this end, a total of 226 individuals of A. australis were collected from the northeast region of Brazil. Our results showed that A. australis inhabited its burrows mainly as pairs, most of which were male-female pairs. In agreement with the expectations, specimens of A. australis were found dwelling as heterosexual pairs more frequently than expected by chance alone. The presence of ovigerous females was associated with the burrow occupation; that is, brooding females were more frequently observed in male-female combinations than solitarily. Also supporting theoretical considerations, we did not observe sexual dimorphism in body size between males and females of the population and the different categories of the burrow occupation. Conversely, sexual dimorphism in cheliped size was evident in the population, with larger chelipeds in males than in females. This observation agrees with that reported for most burrowing shrimps in which male-male competition is the main evolutionary force of sexual selection. The observations above favor the hypothesis that A. australis is primarily monogamous, with a small fraction of the males moderately promiscuous.

The kākāpō (Strigops habroptilus)

The kākāpō, Strigops habroptilus, is a flightless and critically endangered parrot from New Zealand. The species belongs to a unique lineage of parrots, endemic to the archipelago that diverged from other parrots ~82 million years ago (mya), as New Zealand split from Gondwana. The kākāpō genome represents one of the first high-quality chromosome-level reference genomes sequenced by the Vertebrate Genomes Project (VGP) and is an important resource for future studies on evolution and conservation. Analyses of this new genome provide key insights into kākāpō breeding and recovery. Comparison of modern and historical genomes show that kākāpō experienced a reduction in mutational load through genetic drift and purging. These findings indicate that even extremely inbred and bottlenecked species can survive in the wild, but also caution about the future management strategy for the species. Because kākāpō is a taonga, or treasure for Māori, the project was established in collaboration with Te Rūnanga o Ngāi Tahu. The kākāpō genome comprises 23 chromosomes (2n), making for a total genome size of ~1.19 Gbp. It has a repeat content of 15% and a GC content of 42%. A total of 16 053 annotated protein-coding genes were identified. Kākāpō is one of the most inbred species on earth with 0.4–0.5 heterozygote sites per 1000 bp and an inbreeding coefficient (FROH) of ~53%. The kākāpō diverged from flying New Zealand parrots (kea and kākā) ~28 mya. Population genomics analyses revealed that the divergence time between the extinct mainland and the extant Stewart Island populations dates back to the end of the last glaciation ~15 thousand years ago (kya). The kākāpō used to be one of most common and widespread birds in New Zealand. There are now only 202 kākāpō surviving on island sanctuaries that are part of an intense breeding program. Only one mainland bird, called Richard Henry, and 39 Stewart Island birds survived an extreme bottleneck in 1995 and reproduced. Kākāpō are flightless, nocturnal with a probable well-developed sense of smell and with a pronounced sexual dimorphism in body size. Contrary to other parrots, kākāpō have a polygynous lek breeding system. They only reproduce every 2–5 years, during years of heavy rimu (Dacrydium cupressinum) fruiting. Females reach sexual maturity between 5 and 18 years and males between 11 and 23 years. Kākāpō are believed to be exceedingly long-lived, with one male, Richard Henry, having lived up to ~80 years old. The Z sex chromosome fused with the chromosome 11 equivalent of other bird species, and this since has been found for other parrot species, indicating that the fusion may have occurred at the origin of parrots. KINGDOM: Animalia PHYLUM: Chordata CLASS: Aves ORDER: Psittaciformes FAMILY: Psittacidae GENUS: Strigops

Seasonal patterns in behavior and glucocorticoid secretion of a specialist Holarctic tree squirrel (Sciurus aberti).

Seasonally breeding mammals must make constant adjustments in behavior and physiology to manage energetic trade-offs between survival and reproduction. Despite encountering high levels of climate and resource variability across the year, specialist Abert's squirrels (Sciurus aberti), lack the capacity to express hibernation or pronounced morphological adaptations to seasonality. Using accelerometer and GPS devices, we assessed how abiotic environmental factors, reproduction, and resource abundance influenced levels of activity and daily range size in a rural and food-supplemented suburban population of squirrels. We also quantified fecal cortisol metabolites (FCM) in squirrels to assess patterns of glucocorticoid secretion. While changes in weather predicted activity levels in both populations, seasonal variation in activity levels were reduced in food-supplemented compared to rural squirrels. In contrast to activity, daily range size was not affected by weather but was a better predictor of sex-specific reproductive investment. Comparisons between populations suggest that food-supplemented squirrels forage more efficiently within smaller areas. Across both sexes and populations, squirrels showed no sexual dimorphism in body size, no major patterns of seasonal weight change, and no associations between body mass and FCM concentrations; however, FCMs were lower in the food-supplemented compared to rural population during late-spring. Taken together, activity levels and FCM concentrations appear primarily influenced by weather and seasonal fluctuations in food availability, whereas daily range size reflects sexual asymmetries in seasonal reproductive investment. Overall, squirrels appear to rely largely on behavioral adjustments to cope with novel environmental heterogeneity, rather than changes in morphology or GC secretion.

Consequences of hybridization on life history and growth in postmetamorphic Triturus macedonicus

Abstract The Macedonian crested newt T. macedonicus forms a complex hybrid zone with the Balkan crested newt T. ivanbureschi in the central part of the Balkan Peninsula. In this study, we compared life history parameters (sex ratio, survival rate and age of sexual maturation) and growth parameters (body length and mass) of T. macedonicus and T. macedonicus × T. ivanbureschi hybrids over the first three postmetamorphic years. Survival rates were high and similar for both genotypes. Sexual dimorphism in body size (length and mass) was evident at the beginning of the third postmetamorphic year, after the first breeding year, for both T. macedonicus and hybrids. We did not find clear and consistent difference in any of the analysed traits suggesting that hybridization with T. ivabureschi does not affect postmetamorphic growth and survival of T. macedonicus.

Sex-specific thermal tolerance limits in the ditch shrimp Palaemon varians: Eco-evolutionary implications under a warming ocean.

As global temperatures continue to rise due to global change, marine heatwaves are also becoming more frequent and intense, impacting marine biodiversity patterns worldwide. Organisms inhabiting shallow water environments, such as the commercially relevant ditch shrimp Palaemon varians, are expected to be the most affected by rising temperatures. Thus, addressing species' thermal ecology and climate extinction-risk is crucial to foster climate-smart conservation strategies for shallow water ecosystems. Here, we estimated sex-specific upper thermal tolerance limits for P. varians via the Critical Thermal Maximum method (CTmax), using loss of equilibrium as endpoint. We further calculated thermal safety margins for males and females and tested for correlations between upper thermal limits and shrimps' body size. To determine sex-biased variation in P. varians' traits (CTmax, weight and length), we compared trait variation between females and males through the coefficient of variation ratio (lnCVR). Females displayed an average CTmax value 1.8% lower than males (CTmaxfemales=37.0°C vs CTmaxmales=37.7°C). This finding may be related to the larger body size exhibited by females (156% heavier and 39% larger than males), as both length and weight had a significant effect on CTmax. The high energetic investment of females in offspring may also contribute to the differences recorded in thermal tolerance. Overall, organisms with a smaller body-size displayed a greater tolerance to elevated temperature, thus suggesting that smaller individuals may be positively selected in warmer environments. This selection may result in a reduction of size-at-maturity and shifts in sex ratio, given the sexual dimorphism in body size of shrimps. The thermal safety margin of P. varians was narrow (∼2.2°C for males and ∼1.5°C for females), revealing the vulnerability of this species to ocean warming and heatwaves.

Rapid evolution of sexual size dimorphism facilitated by Y-linked genetic variance.

Sexual dimorphism is ubiquitous in nature but its evolution is puzzling given that the mostly shared genome constrains independent evolution in the sexes. Sex differences should result from asymmetries between the sexes in selection or genetic variation but studies investigating both simultaneously are lacking. Here, we combine a quantitative genetic analysis of body size variation, partitioned into autosomal and sex chromosome contributions and ten generations of experimental evolution to dissect the evolution of sexual body size dimorphism in seed beetles (Callosobruchus maculatus) subjected to sexually antagonistic or sex-limited selection. Female additive genetic variance (VA) was primarily linked to autosomes, exhibiting a strong intersexual genetic correlation with males ([Formula: see text] = 0.926), while X- and Y-linked genes further contributed to the male VA and X-linked genes contributed to female dominance variance. Consistent with these estimates, sexual body size dimorphism did not evolve in response to female-limited selection but evolved by 30-50% under male-limited and sexually antagonistic selection. Remarkably, Y-linked variance alone could change dimorphism by 30%, despite the C. maculatus Y chromosome being small and heterochromatic. Our results demonstrate how the potential for sexual dimorphism to evolve depends on both its underlying genetic basis and the nature of sex-specific selection.

Low size dimorphism does not lead to reduced sexual segregation: exploring effects of habitat divergence and activity

While the proximate and ultimate causes of sexual segregation have been well studied over the past 30 years, most of the research has focused on species with a pronounced sexual size dimorphism. Species with a smaller size dimorphism are probably understudied, because the assumption is that aggregation rather than sex segregation should be the norm. We used 6 years of direct observations of goitered gazelles, Gazella subgutturosa , an ungulate with a small degree of sexual size dimorphism, to explore sexual segregation and aggregation patterns and habitat choice at two timescales. We predicted minimal differences in activity budgets between the sexes, based on their small size dimorphism, and did not expect any evolutionary niche divergence based on size. However, we found that goitered gazelles showed considerable sexual and habitat segregation for most of the year, and only showed a tendency to randomly aggregate during the peak of the rutting season. We also found that they segregated socially and by habitat and had different activity budgets in some months. Behavioural asynchrony and sexual differences in habitat use were much greater than predicted for a species with such a small sexual dimorphism in body size. Our study confirms strong multifactorial sexual segregation patterns, and points to the potential importance that social factors (aggression and territoriality) may have on sexual segregation in goitered gazelles. • Studies on sexual segregation mostly focus on highly sexual size-dimorphic species. • High degree of sexual segregation was found in a less size-dimorphic species. • Both habitat differentiation and activity are associated with sexual segregation. • Goitered gazelles exhibit multifactorial segregation patterns.

Effects of Sex and Breeding Status on Skull Morphology in Cooperatively Breeding Ansell’s Mole-Rats and an Appraisal of Sexual Dimorphism in the Bathyergidae

African mole-rats of the genus Fukomys (Northern common mole-rats) combine a monogamous mating system and pronounced sexual size dimorphism; a pattern highly untypical for mammals. At the same time, they live in cooperatively breeding groups composed of reproductive and non-reproductive members of both sexes. How and to which degree sex and breeding status influence morphofunctional characters in eusocial mole-rats is not well characterized but essential to come to a comprehensive understanding of their peculiar social system. Here, we explore patterns of morphological differentiation in skulls of Ansell’s mole-rats (Fukomys anselli) by means of multivariate analysis of linear skull measurements combined with a 2D shape analysis of cranium and mandible. Compared to females, males display larger skulls relative to body size and show an expansion of the facial portion of the cranium, while reproductive status did not have an effect on any of the traits studied. We also show that species of Fukomys mole-rats display a scaling of relative sexual body size dimorphism in compliance to Rensch’s rule, which is deemed indicative of intense male intrasexual competition. For the bathyergid family as a whole, results of scaling analyses were more ambiguous, but also indicative of Rensch’s rule conformity. In line with genetic field data, our results point to a greater role of male-male conflicts in Fukomys than is traditionally assumed and support the notion that reproductive status does not correlate with morphofunctional segregation in these unusual rodents.

Morphometric differentiation and sexual dimorphism in Limnomedusa macroglossa (Duméril & Bibron, 1841) (Anura: Alsodidae) from Uruguay

Intersexual morphological differences within a species occur in many traits, including body size and shape. Many processes that cause geographic variability in morphology have been proposed: population structure, phenotypic plasticity (environmental effects on development), and natural and/or sexual selection. Several hypotheses can explain patterns of sexual dimorphism in anurans, including natural or intra/inter-sexual selection, and differences in life history strategies between sexes. Limnomedusa macroglossa is considered a habitat specialist restricted to rocky outcrops in Brazil, Argentina, Paraguay, and Uruguay. We evaluated the extent of sexual (size and shape) dimorphism in L. macroglossa from Uruguay based on morphometrics and secondary sexual characteristics, while taking into account geographic variation. Sexual dimorphism in body size of adults was found, but multivariate analyses did not demonstrate the existence of significant differences in shape. There were also significant differences in body size and hind leg measurements among six hydrographic basins as a result from the phenotypic plasticity correlated with local temperature, representing a clinal variation along the latitudinal gradient of Uruguay. The sexual dimorphism found in body size is probably the consequence of higher growth rates and/or late sexual maturity in females, which favors larger body size for accommodating larger ovaries, and thus, higher reproductive output.

Does posture explain the kinematic differences in a grounded running gait between male and female Svalbard rock ptarmigan (Lagopus muta hyperborea) moving on snow?

The majority of locomotor research is conducted on treadmills and few studies attempt to understand the differences between this and animals moving in the wild. For example, animals may adjust their gait kinematics or limb posture, to a more compliant limb, to increase stability of locomotion to prevent limb failure or falling on different substrates. Here, using video recordings, we compared locomotor parameters (speed range, stride length, stride frequency, stance duration, swing duration and duty factor) of female Svalbard rock ptarmigan (Lagopus muta hyperborea) moving in the wild over snow to previous treadmill-based research. We also compared the absolute and body size (body mass and limb length)-corrected values of kinematic parameters to published data from males to look for any sex differences across walking and grounded running gaits. Our findings indicate that the kinematics of locomotion are largely conserved between the field and laboratory in that none of the female gaits were drastically affected by moving over snow, except for a prolonged swing phase at very slow walking speeds, likely due to toe dragging. Comparisons between the sexes indicate that the differences observed during a walking gait are likely due to body size. However, sexual dimorphism in body size could not explain the disparate grounded running kinematics of the female and male ptarmigan, which might be linked to a more crouched posture in females. Our findings provide insight into how males and females moving in situ may use different strategies to alleviate the effects of a variable substrate.

Limits to the exaggeration and diversification of a male sexual trait in the false blister beetle Oedemera sexualis

AbstractDifferentiation in sexual traits among populations is one of the major predictions of theories of sexual selection and sexual conflict. A balance between maximizing reproductive benefits and minimizing survival costs could explain variation in sexual traits within and between populations. The false blister beetle Oedemera sexualis (Coleoptera: Oedemeridae) has exaggerated sexual traits, that is, sexually dimorphic hindlegs. In this study, we characterized scaling relationships in populations of O. sexualis to evaluate the determinants of sexual trait variation in the species. We quantified sexual dimorphism in body size and hindleg sizes in three representative populations based on distance measurements and an elliptical Fourier analysis. We found significant variation in the degree of sexual dimorphism for body and hindleg sizes among populations. In particular, differentiation in the male hind femur shape, especially the femur width, was conspicuous. Scaling relationships between male hind femur width and body size were best described by logistic models, showing that increases in male hind femur width were constrained for large individuals in all three populations. The degree of constrained growth of the hind femur width differed among populations in accordance with the population means, while the basal growth rates did not. Populations with smaller mean values for sexual traits showed more limited sexual trait exaggeration, contrary to the predictions based on resource competition among body parts. The latitudinal cline in femur widths suggests that environmental constraints on exaggeration might be responsible for sexual trait diversification in O. sexualis.

How long does it take to know a species? Redescription, vocalization, and chigger mites infestation pattern in the centenary emBrachycephalus/em emgarbeanus/em (Anura: Brachycephalidae).

Although we celebrate the centennial of Brachycephalus garbeanus' discovery, little progress has been done on understanding this species' biology apart from a few morphological and ecological studies, which includes its redescription based on three specimens from the type-series, microhabitat use, sexual dimorphism in body size, and feeding habits. This species is endemic to the Serra dos Órgãos Mountain range, in the state of Rio de Janeiro, southeastern Brazil. Here we redescribe B. garbeanus based on a wide sampling, including its advertisement and aggressive calls, and also the chigger mites infestation pattern. The advertisement call is longer than 25.8 s with pulsed notes series emitted at an average rate of 2.3 notes/s and 14.1 pulses/s; long inter-note interval with 320 ms; notes with distinctly short pulses (1 to 16 ms); low dominant frequency for this genus (3.0-5.4 kHz) and presence of four harmonics. This species is often parasitized by chigger mites of Hannemania, with a prevalence of infection of 67%, mainly affecting the ventral body surface. Females had a higher prevalence of parasites than males and there was no correlation found between the size of specimens and the number of parasites. Our study, provides an important and overdue taxonomical contribution, including a large amount of novel information for B. garbeanus.

Reproductive Biology and Sexual Dimorphism in Bokermannohyla alvarengai (Anura: Hylidae)

The general pattern of sexual size dimorphism (SSD) in amphibians is characterized by females being larger than males. However, the reverse pattern, a male-biased SSD, may be widespread within some particular groups, as seems to be the case for the Neotropical treefrog genus Bokermannohyla. Although SSD is commonly associated with factors influential to breeding success, the evolutionary determinants of SSD remain controversial. Thus, the study of SSD, particularly on lesser-known species, remains critical to advance our understanding of the evolution of body size and other traits associated with the reproductive biology of amphibians. Herein, we examined the occurrence of sexual dimorphism in body size and other morphometric attributes in Bokermannohyla alvarengai and provided a detailed account of its reproductive biology. This species is endemic to a threatened habitat, occurs at low densities, and has a poorly documented natural history. We found that, at maturity, males of B. alvarengai were larger than females, with hypertrophied forelimbs and larger prepollex spines. This set of features, common to other Bokermannohyla species, is often attributed to the occurrence of male territorial defense and aggression between males. We found that B. alvarengai has a prolonged breeding season that extends from the middle of the dry season to the middle of the rainy season. Adult males did not form breeding aggregations and seemed to establish and defend territories; these males often had skin scars indicative of male–male combat. However, alternative interpretations for differences in body size and secondary sexual characters cannot be ruled out and are discussed.

Mating System of the Snapping Shrimp Synalpheus brevicarpus (Caridea, Alpheidae) Inhabiting Sponges Dysidea sp. (Demospongiae).

AbstractThe lifestyle of symbiotic species in the genus Synalpheus can vary from pair living to eusocial. A pair-living social system commonly implies the adoption of a monogamous mating system. In this study, we used the symbiotic shrimp Synalpheus brevicarpus in association with the sponge Dysidea sp. to test the hypothesis that heterosexual pairs of symbiotic shrimps can adopt a monogamous mating system when living in association with a morphologically complex host. We collected a total of 40 sponges, which were inhabited by 76 shrimps: 41 males, 33 females, and 2 juveniles. Synalpheus brevicarpus is sexually dimorphic, with males displaying proportionately larger weaponry (snapping claws) and a smaller average body size than females. Sponges were more often inhabited by a pair of heterosexual shrimps than expected by chance. Larger sponges were inhabited by more than one pair of shrimps in which the sex ratio did not differ significantly from 1∶1. Pairs of heterosexual shrimps were recorded, with females carrying embryos in all stages of embryonic development. Our results indicate that S. brevicarpus is a pair-living shrimp with a monogamous social and mating system that may also guard spaces or areas within its sponge host. Our hypothesis of monogamy is supported by the observations on pair living, sex ratio, and sexual dimorphism in body size and weaponry in this species.