Reverse Sexual Dimorphism Research Articles

Tawny Owls Strix aluco from a southern European population differ in size and degree of reverse sexual dimorphism from northern European counterparts

ABSTRACT Tawny Owls in southern Europe were trapped and measured. Compared to males, the females were larger, heavier, and more greyish in colour, but there was a large biometric overlap. The variable with the highest Storer’s dimorphism index (SDI) was weight, though our population had one of the smallest dimorphisms observed in Europe for weight. It has been proposed that differences in diet could lead to differing behaviour and, in consequence, the observed dimorphism degree (SDI) by natural selection.

Non-Invasive Sex Determination of Nestlings and Adult Bonelli’s Eagles Using Morphometrics

Biometric analysis allows the sexing of most vertebrates, particularly birds. Birds of prey, and, especially, the Bonelli's eagle (Aquila fasciata), show reverse sexual dimorphism (i.e., females are usually larger than males). In contrast to blood sampling, the use of morphometrics allows sex determination using a non-invasive method, and, therefore, it facilitates fieldwork. By means of a linear discriminant analysis of biometric variables, we obtained different equations that allow the sexing of nestlings and adult Bonelli's eagles. We sampled 137 Bonelli's eagles, 82 nestlings and 55 adults in eastern Spain during the period 2015-2022. The sexes obtained after linear discriminant analysis were compared with their molecular sexing. The validation procedure of the linear discriminant equations facilitated the reduction of the number of variables used and, consequently, optimised working time and sexing accuracy. After validation, some equations showed a 100% sexing efficiency for Bonelli's eagles, particularly for adults. Our results showed that the variables with smaller overlap between the sexes were the lateral tarsus length and dorso-ventral tarsus length, particularly in nestlings. The rest of the variables showed some overlap between the sexes in both age classes. The results we obtained enable the sexing of juvenile and adult Bonelli's eagles in the field using just these two measurements. Hence, this is an easy, accurate, quick and non-invasive method with multiple applications, including in studies on population dynamics, survival analysis or extinction risk assessments, which, ultimately, could contribute to the improvement of the conservation status of this endangered species.

(Not) far from home: No sex bias in dispersal, but limited genetic patch size, in an endangered species, the Spotted Turtle (Clemmys guttata).

Sex-biased dispersal is common in many animals, with male-biased dispersal often found in studies of mammals and reptiles, including interpretations of spatial genetic structure, ostensibly as a result of male-male competition and a lack of male parental care. Few studies of sex-biased dispersal have been conducted in turtles, but a handful of studies, in saltwater turtles and in terrestrial turtles, have detected male-biased dispersal as expected. We tested for sex-biased dispersal in the endangered freshwater turtle, the spotted turtle (Clemmys guttata) by investigating fine-scale genetic spatial structure of males and females. We found significant spatial genetic structure in both sexes, but the patterns mimicked each other. Both males and females typically had higher than expected relatedness at distances <25 km, and in many distance classes greater than 25 km, less than expected relatedness. Similar patterns were apparent whether we used only loci in Hardy-Weinberg equilibrium (n=7) or also included loci with potential null alleles (n=5). We conclude that, contrary to expectations, sex-biased dispersal is not occurring in this species, possibly related to the reverse sexual dimorphism in this species, with females having brighter colors. We did, however, detect significant spatial genetic structure in males and females, separate and combined, showing philopatry within a genetic patch size of <25 km in C.guttata, which is concerning for an endangered species whose populations are often separated by distances greater than the genetic patch size.

Bioaccumulation of mercury is equal between sexes but different by age in seabird (Sula leucogaster) population from southeast coast of Brazil

Since several seabird species have sexual size dimorphism, in which one sex is larger than the other, and may consume bigger prey, this size difference may affect the contamination concentration in the seabird’s tissues depending on their sex and age. In this study, mercury contamination was investigated in brown booby (Sula leucogaster) adults and juveniles during their breeding season at the Santana Archipelago, on the southeast coast of Brazil. Two hypotheses were evaluated: 1. As females consume larger prey than males due to the reverse sexual dimorphism, higher total mercury (THg) and methylmercury (MeHg) concentrations are expected in females tissues than in males; 2. Adult seabirds have more time to accumulate mercury than juveniles, so it is expected that adults will show higher THg and MeHg concentrations than juveniles in their feathers, but none in blood since the last indicates the exposure of short time (30–60 days), as it is a constantly synthesized tissue. Feathers and blood were sampled from 20 individuals of each group (males, females and juveniles). Also, 10 eggs of the brown booby and muscle tissue samples of their main prey were collected, from February to October 2018. Females and males had similar THg concentrations in the tissues with no statistical differences between sexes. Thus, the sexual size dimorphism did not influence mercury concentrations among the tissues and both genders can be used as a biomonitor. Brown booby juveniles had low THg and MeHg concentrations compared to adults due to a shorter time of exposure for mercury to bioaccumulate in their tissues. This is the first study, to the best of our knowledge, analyzing methylmercury in feathers, blood and eggs of a tropical seabird, which can be a useful baseline for future studies on the effects of contaminants on this species in tropical regions.

Population biology of the unusual thermoconforming lizards of the Andes Mountains of Peru (Squamata: Gymnophthalmidae)

AbstractMontane animals require different adaptations than lowland species because of more severe conditions. Proctoporus lizards of the Andes Mountains experience cold temperatures year‐round, which may affect their activity. Two species of this poorly known genus, P. unsaacae and P. sucullucu, have similar morphology and ecology, but had never been studied in detail. The purpose of this project was to compare the population biology of the two species and to ascertain whether they were more likely to share ecological similarities with phylogenetic relatives or with other unrelated lizards of the Andes. We established two permanent plots in the Sacred Valley of the Incas in Cusco region, Peru, and examined the thermal ecology, movement, sex ratio, longevity, population sizes, growth patterns, reproduction and other factors over a period of 4 years. Proctoporus unsaacae and P. sucullucu were similar in most aspects of their ecology except that P. sucullcu was larger, had smaller population sizes, and fewer recaptures. Both species live exclusively under rocks and are strict thermoconformers who do not actively thermoregulate their body temperatures by basking, as other high Andean lizards do. The two species have reverse sexual dimorphism with P. unsaacae having larger females and P. sucullcu having larger males. The species are highly philopatric with average movement of less than 7 m in a lifetime. Both appear to be relatively long‐lived with an individual P. unsaacae living longer than 2 years 8 months. At both sites, populations age structures had few juveniles and we detected a declining population of P. unsaacae in Urubamba. This project lays the groundwork for more in‐depth studies of the ecology of both species and their high‐elevation habitats.

Infestation Of Bopyrid Isopod Parasite (Bopyridae) on ‘Coral Banded Boxing’ Shrimp Stenopus hispidus Olivier, 1811 (Stenopodidae) in the Lakshadweep Archipelago

Bopyrid parasitic isopods (family Bopyridae Rafinesque) are unique and well known to utilize marine crustaceans as both intermediate and definitive host during their life cycle 1,2 . The family Bopyridae is the largest and highly diverse group with 605 species under 8 subfamilies 2,3 . The males are smaller than females (exhibiting reverse sexual dimorphism) and are attached to the ventral posterior region of the female abdomen 4 . Bopyrids used to infest either branchially or abdominally on a variety of crustaceans including brachyurans, anomurans, penaeids and carideans 1,2,5–7 . Infestation of parasites has deleterious effects on host such as reduction in growth, energy and mainly resulting in reproductive failures 8–11 . It can also affect the escape response of host to predators 12 . Extensive studies have revealed bopyrid parasite infestation on caridean shrimps 3 . However, the infestation of parasite on Stenopodidean shrimps has been rarely documented 10,13–15 . The present contribution is one such rare observation on the infestation of bopyrid isopod parasite on the marine ornamental shrimp Stenopus hispidus from Lakshadweep.

Multidirectional sexual dimorphism for the live weight in domestic pigs

In mammals, males are typically larger and heavier than females. In particular, the average weight of wild boar females is about 80% of that of the males. In a vast majority of domestic swine populations (breeds, populations of breeding groups), this value varies from 70 to 91% (the central value of the range of variation of 81%). However, there are three genealogically continuous groups of domestic pigs (Vietnamese Masked breed MY, minisibs and Svetlogorsk mini-pigs) that make exceptions. Their specific feature is the reverse sexual dimorphism in weight – mature females are heavier than males. This phenomenon, not typical of the species Sus scrofa, was the reason for the present study. Although this research is preliminary, some assumptions can be made. Firstly, the ratio of the weight of mature females to the weight of mature males is obviously characteristic of the species, deviations from which repressed stabilizing selection. Second, in domestic pigs, normal and reverse sexual dimorphism in weight may be different in nature: in the former case, it is a great length of the period of intensive growth in males, in the latter, a large growth rate of females during the first year of life. The third characteristic of domestic pigs in Southeast Asia, early puberty, may be due to a consistent use of young and therefore small-sized males for reproduction purposes; however, the small size due to their youth, cannot be a target of artificial selection – nor can they be the cause of reverse sexual dimorphism in weight. Finally, reverse sexual dimorphism may be due to a tendency towards early obesity in females, which might be to a single mutation as its genetic cause.

The sexual and mating system of the shrimp Odontonia katoi (Palaemonidae, Pontoniinae), a symbiotic guest of the ascidian Polycarpa aurata in the Coral Triangle.

Theory predicts that monogamy is adaptive in symbiotic crustaceans inhabiting relatively small and morphologically simple hosts in tropical environments where predation risk away from hosts is high. We tested this prediction in the shrimp Odontonia katoi, which inhabits the atrial chamber of the ascidian Polycarpa aurata in the Coral Triangle. Preliminary observations in O. katoi indicated that males were smaller than females, which is suggestive of sex change (protandry) in some symbiotic organisms. Thus, we first investigated the sexual system of O. katoi to determine if this shrimp was sequentially hermaphroditic. Morphological identification and size frequency distributions indicated that the population comprised males that, on average, were smaller than females. Gonad dissections demonstrated the absence of transitional individuals. Thus, O. katoi is a gonochoric species with reverse sexual dimorphism. The population distribution of O. katoi in its ascidian host did not differ significantly from a random distribution and shrimps inhabiting the same host individual as pairs were found with a frequency similar to that expected by chance alone. This is in contrast to that reported for other socially monogamous crustaceans in which pairs of heterosexual conspecifics are found in host individuals more frequently than expected by chance alone. Thus, the available information argues against monogamy in O. katoi. Furthermore, that a high frequency of solitary females were found brooding embryos and that the sex ratio was skewed toward females suggests that males might be roaming among hosts in search of receptive females in O. katoi. Symbiotic crustaceans can be used as a model system to understand the adaptive value of sexual and mating systems in marine invertebrates.

Social monogamy in the crab Planes major, a facultative symbiont of loggerhead sea turtles

Studying how host characteristics and ecology affect the mating systems of symbiotic crustaceans offers an opportunity to understand how ecological factors contribute to the evolution of different animal mating systems. In theory, symbiotic crustaceans should display social monogamy with long-term heterosexual pairing when hosts are relatively small in body size and structurally simple, and when hosts have relatively low abundance in habitats where the risk of mortality for symbionts (e.g., predation) away from hosts is high. We test this prediction in the mating system of the flotsam crab (Planes major) and its facultative association with loggerhead sea turtles (Caretta caretta). First, we found that the overall population and sex distributions were non-random and crabs inhabited host turtles as heterosexual pairs more frequently than expected by chance, which supports the hypothesis that P. major is socially monogamous on C. caretta. Second, we found that male crabs pair with females regardless of their reproductive state, male–female pairs do not display size-assortative pairing, crab body size and host turtle body size are not correlated, and crabs display reverse sexual dimorphism in body size and conventional sexual dimorphism in weaponry. These results do not support the hypothesis that social monogamy in P. major is always long term. Instead, our results suggest that the duration of social monogamy in P. major is likely variable and may involve some degree of host switching and intra-sexual (mostly male–male) competition. Our results were only partially consistent with theoretical considerations for how host characteristics and ecology affect the mating systems of symbiotic crustaceans, and future studies should focus on quantifying the degree and direction of host switching to better understand the factors that affect the duration of monogamous pairing when P. major associates with C. caretta.

Variation in offspring sex ratio of a long‐lived sexually dimorphic raptor, the Eastern Imperial Eagle Aquila heliaca

Sex ratio theory attempts to explain observed variation in offspring sex ratio at both the population and the brood levels. In the context of low‐fecundity organisms producing high‐investment offspring, the drivers of adaptive variation in sex ratio are incompletely understood. For raptors that display reverse sexual dimorphism (RSD), preferential allocation of resources to the putatively cheaper sex (male) may be a response to environmental, social or demographic stressors. To assess the extent of skew in offspring sex ratios and to evaluate possible dietary, environmental and demographic correlates of such skew to long‐lived RSD avian species, we evaluated the offspring sex ratio of 219 chicks from 119 broods in 30 territories of Eastern Imperial Eagles Aquila heliaca across 7 years and four regions at a nature reserve in Kazakhstan. Only in one region in 1 year of our study did the offspring sex ratio differ significantly from parity (10 males : 1 female in 11 territories). Whereas offspring sex ratios were independent of dietary diversity, precipitation, temperature and productivity, we found that year had a moderate effect on brood sex ratio within territories. Our results provide limited evidence of brood sex manipulation in these populations of Eastern Imperial Eagles, and no mechanistic insight into predictions associated with it. Stochastic variation is likely to explain much of the fluctuation we observed in sex ratios, but our observations are also consistent with the hypothesis that sex‐ratio manipulation may occur irregularly, in concurrence with atypical environmental or demographic conditions that fluctuate at a time scale longer than that of our 7‐year study.

Effect of prey availability on growth-rate trajectories of an aquatic predator, the viperine snake Natrix maura

The energy gained by an organism is used for maintenance, growth and reproduction. In habitats with limited resources, these processes compete for available energy and may induce intraspecific variation in body condition, growth trajectories and reproductive output. We tested the hypothesis that populations exposed to higher food availability are able to grow faster, and attain larger body sizes in the viperine snake (Natrix maura). We estimated snake age by counting growth lines in the skull’s ectopterygoid bone, and compared body size growth curves from three Iberian populations exposed to temporal variation of food resources availability. In the three localities, and in males and females, the growth curves followed a quadratic function that tended to an asymptotic value as growth slowed down. Growth curves showed slower growth rates and an early asymptote for males, in agreement with the reverse sexual dimorphism in body size of this species. We also detected interpopulational differences, with the Ebro Delta population exhibiting slower growth rates and smaller asymptotic body size in both sexes. This population inhabits rice fields with an artificial waterflow cycle, a condition that implies a shorter period of prey availability for snakes, compared to the other two populations, where prey is available for longer periods of time. Moreover, high proportion of snakes with tail breakage in this population indicated high predation pressure. These environmental conditions suggest that food availability and predation pressure may be concurrently acting to produce smaller N. maura at the Ebro Delta than at the other two populations.

The Enigmatic Life History of the Symbiotic Crab Tunicotheres moseri (Crustacea, Brachyura, Pinnotheridae): Implications for Its Mating System and Population Structure

Resource-monopolization theory predicts the adoption of a solitary habit in species using scarce, discrete, and small refuges. Life-history theory suggests that temporarily stable parental dwellings favor extended parental care in species that brood embryos. We tested these two predictions with the symbiotic crab Tunicotheres moseri. This species exhibits abbreviated development and inhabits the atrial chamber of the scarce, structurally simple, long-lived, and relatively small ascidian Phalusia nigra in the Caribbean. These host characteristics should favor a solitary habit and extended parental care (EPC) in T. moseri. As predicted, males and females of T. moseri inhabited ascidians solitarily with greater frequency than expected by chance alone. The male-female association pattern and reverse sexual dimorphism (males < females) additionally suggests a promiscuous "pure-search" mating system in T. moseri. Also in agreement with theoretical considerations, T. moseri displays EPC; in addition to embryos, females naturally retain larval stages, megalopae, and juveniles within their brooding pouches. This is the first record of EPC in a symbiotic crab and the second confirmed record of EPC in a marine brachyuran crab. This study supports predictions central to resource-monopolization and life-history theories.

Sexual and mating system in a caridean shrimp symbiotic with the winged pearl oyster in the Coral Triangle

AbstractFor symbiotic crustaceans, theory predicts that monogamy is adaptive when species inhabit scarce, relatively small and morphologically simple hosts in tropical environments where predation risk away from hosts is high. We tested this prediction in the shrimp Paranchistus pycnodontae, which inhabits the mantle cavity of the winged pearl oyster Pteria penguin in the Coral Triangle. In various symbiotic crustaceans, males are smaller than females, and this sexual dimorphism has been used as evidence of sex change (protandry) in these organisms. Preliminary observations in Pa. pycnodontae suggested that males were smaller than females. Thus, we first investigated the sexual system of Pa. pycnodontae to determine if the species was protandric. Morphological identification and size frequency distributions indicated that the population comprised small males, small immature females and larger mature females, which was confirmed by dissections. No transitional individuals were found. Thus, Pa. pycnodontae is a gonochoric species with reverse sexual dimorphism. Pa. pycnodontae inhabit as heterosexual pairs in the mantle cavity of hosts more frequently than is expected by chance alone. Pairing was size assortative; both carapace length and propodus length of the major cheliped were positively correlated between males and females forming pairs. Males occur with females in the same host, independent of the female gravid condition or of the stage of development of the brooded eggs. Lastly, the major cheliped did not exhibit positive allometry in males. All the available information suggests that Pa. pycnodontae has adopted a socially monogamous mating system with males and females forming exclusive pairs from other adults. Symbiotic shrimps can be used as a model system to understand behavioural diversity within socially monogamous marine invertebrates.

Sex differences in telomeres and lifespan

Males and females often age at different rates resulting in longevity 'gender gaps', where one sex outlives the other. Why the sexes have different lifespans is an age-old question, still fiercely debated today. One cellular process related to lifespan, which is known to differ according to sex, is the rate at which the protective telomere chromosome caps are lost. In humans, men have shorter lifespans and greater telomere shortening. This has led to speculation in the medical literature that sex-specific telomere shortening is one cause of sex-specific mortality. However, telomere shortening may be a cause for and/or a consequence of the processes that govern survival, and to infer general principles from single-taxon studies may be misleading. Here, we review recent work on telomeres in a variety of animal taxa, including those with reverse sexual lifespan dimorphism (i.e., where males live longer), to establish whether sex-specific survival is generally associated with sex differences in telomere dynamics. By doing this, we attempt to tease apart the potential underlying causes for sex differences in telomere lengths in humans and highlight targets for future research across all taxa.

Resource partitioning by species but not sex in sympatric boobies in the central Pacific Ocean

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 403:291-301 (2010) - DOI: https://doi.org/10.3354/meps08478 Resource partitioning by species but not sex in sympatric boobies in the central Pacific Ocean Hillary S. Young1,*, Scott A. Shaffer2,5, Douglas J. McCauley1, Dave G. Foley3,4, Rodolfo Dirzo1, Barbara A. Block1 1Department of Biology, Stanford University, 371 Serra Mall, Stanford, California 94305, USA 2Ecology & Evolutionary Biology, University of California Santa Cruz, Santa Cruz 95060, USA 3Joint Institute for Marine and Atmospheric Research, University of Hawaii, Honolulu, Hawaii 96822, USA 4NOAA/NMFS/SWFSC/Environmental Research Division, 1352 Lighthouse Avenue, Pacific Grove, California 93950-2097, USA 5Present address: Department of Biological Sciences, San José State University, San José, California 95192, USA *Email: hsyoung@stanford.edu ABSTRACT: Sympatric species with similar ecological requirements and differences in body size would be expected to partition resources to facilitate coexistence. For sexually dimorphic species, we may expect resource partitioning by gender as well as by species identity. However, it is difficult to document species and sexual resource partitioning in marine ecosystems, given the intractability of these systems and the vagility of many marine animals. Here, we examined differences in the foraging behavior and prey selection of 2 congeneric and coexisting seabird species—masked boobies Sula dactylatra and red-footed boobies Sula sula—on Palmyra Atoll in the equatorial Pacific Ocean. These seabirds exhibit substantial size dimorphism between species and also have reverse sexual dimorphism within species. Pronounced interspecific differences in foraging patterns were observed with high-resolution GPS tracking devices, where smaller red-footed boobies conducted longer foraging trips (in both time and distance). Red-footed boobies also had more frequent landings on the sea surface, slower mean and maximum travel speeds, and more westerly trip azimuths. Stable isotope and diet analyses produced data that complemented returns from electronic tagging. Stable isotope ratios of carbon indicated that masked boobies foraged on prey with a less pelagic δ13C signature compared to red-footed boobies. In contrast, no gender differences were identified in any foraging parameters. The mechanisms for maintenance of these pronounced differences in niche partitioning across species were not explicitly examined, yet the data suggest physiological variation across species may be a more plausible mechanism than competitive interactions. KEY WORDS: Resource partitioning · Reverse sexual dimorphism · Foraging ecology · GPS tracking · Sula sula · S. dactylatra Full text in pdf format PreviousCite this article as: Young HS, Shaffer SA, McCauley DJ, Foley DG, Dirzo R, Block BA (2010) Resource partitioning by species but not sex in sympatric boobies in the central Pacific Ocean. Mar Ecol Prog Ser 403:291-301. https://doi.org/10.3354/meps08478 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 403. Online publication date: March 22, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Nuclear DNA sequences detect species limits in ancient moa.

Ancient DNA studies have typically used multi-copy mitochondrial DNA sequences. This is largely because single-locus nuclear genes have been difficult to recover from sub-fossil material, restricting the scope of ancient DNA research. Here, we have isolated single-locus nuclear DNA markers to assign the sex of 115 extinct moa and, in combination with a mitochondrial DNA phylogeny, tested competing hypotheses about the specific status of moa taxa. Moa were large ratite birds that showed extreme size variation both within and among species. For some taxa, this large variation was hypothesized to represent sexual dimorphism, while for others it was argued to reflect the existence of different species. Our results show that moa were characterized by extreme reverse sexual dimorphism and as a result we have been able to clarify the number of moa species. For example, we show that the three recognized 'species' of Dinornis comprised only two monophyletic groups and that two of these 'species' comprised individuals of one sex only. This study also illustrates that single-locus nuclear DNA sequences can be consistently recovered from ancient material.