Sexual size dimorphism (SSD) is caused by differences in selection pressures and life‐history trade‐offs faced by males and females. Proximate causes of SSD may involve sex‐specific mortality, energy ...acquisition, and energy expenditure for maintenance, reproductive tissues, and reproductive behavior. Using a quantitative, individual‐based, eco‐genetic model parameterized for North Sea plaice, we explore the importance of these mechanisms for female‐biased SSD, under which males are smaller and reach sexual maturity earlier than females (common among fish, but also arising in arthropods and mammals). We consider two mechanisms potentially serving as ultimate causes: (a) Male investments in male reproductive behavior might evolve to detract energy resources that would otherwise be available for somatic growth, and (b) diminishing returns on male reproductive investments might evolve to reduce energy acquisition. In general, both of these can bring about smaller male body sizes. We report the following findings. First, higher investments in male reproductive behavior alone cannot explain the North Sea plaice SSD. This is because such higher reproductive investments require increased energy acquisition, which would cause a delay in maturation, leading to male‐biased SSD contrary to observations. When accounting for the observed differential (lower) male mortality, maturation is postponed even further, leading to even larger males. Second, diminishing returns on male reproductive investments alone can qualitatively account for the North Sea plaice SSD, even though the quantitative match is imperfect. Third, both mechanisms can be reconciled with, and thus provide a mechanistic basis for, the previously advanced Ghiselin–Reiss hypothesis, according to which smaller males will evolve if their reproductive success is dominated by scramble competition for fertilizing females, as males would consequently invest more in reproduction than growth, potentially implying lower survival rates, and thus relaxing male–male competition. Fourth, a good quantitative fit with the North Sea plaice SSD is achieved by combining both mechanisms while accounting for sex‐specific costs males incur during their spawning season. Fifth, evolution caused by fishing is likely to have modified the North Sea plaice SSD.
The paper presents a model to evolutionarily explain the sexual size dimorphism with an eco‐genetic model adapted to detailed empirical data of North Sea plaice. Behavioral investments and diminishing fitness returns are considered as alternative explanations with its implication in individual energy allocation, and put into context with the ecology of the species.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
One fundamental question in biology is how animals control their proper body size. Hippo signaling pathway has emerged as an evolutionarily conserved network to regulate organ size from Drosophila to ...mammals. Interestingly, our previous study has also implied the roles of hippo signaling in Chinese tongue sole (Cynoglossus semilaevis), a flatfish exhibiting female-biased sexual size dimorphism (SSD). Specifically, two yes-associated protein 1 (yap1) homologs, key effectors within hippo signaling, exhibited the opposite expression pattern in the female and male gonads of C. semilaevis. Whether and how these two yap1 genes participate in female-biased SSD is unknown. In the present study, phylogenetic tree analysis firstly designated these two yap1 genes as yap1 and yap1b, with no taz gene available in C. semilaevis. Subsequent quantitative PCR analysis demonstrated that yap1 exhibited the highest expression levels within the male gonad at three-month-old, while the predominant expression of yap1b was detected in the female gonad at two-year-old. The co-localization of yap1 and yap1b was observed in the cytoplasm of oocyte and sperm. Cebpα, a negative regulator for dmrt1, exhibited positive and negative regulation on the yap1 and yap1b, respectively. Myog, a crucial transcription factor for myogenesis, specifically binded and activated yap1b promoter, not yap1. Furthermore, DAP-seq revealed the regulatory networks of yap1 and yap1b in C. semilaevis. Importantly, many growth and reproduction-related pathways, including the JAK-STAT signaling pathway, prolactin signaling pathway, axonal regeneration, and steroid hormone synthesis, were included in the common peaks of yap1 and yap1b. Moreover, the application of verteporfin reagents into testis and ovary cells resulted in a decrease in yap1 and yap1b levels. Consequently, the expression of growth hormone receptor (ghr), growth hormone actin α (smtla), estrogen receptor (esr2b), and 17β-hydroxysteroid dehydrogenase type 7 (hsd17b7), were also affected. In addition, the administration of verteporfin on C. semilaevis caused a significant reduction in growth rate. These findings provided insights into the role of the hippo signaling pathway in regulating SSD of C. semilaevis.
•Yap1 and yap1b were identified in C. semilaevis, with no taz gene.•The co-localization of yap1 and yap1b was observed in the cytoplasm of oocyte and sperm.•Cebpα, a negative regulator for dmrt1, showed positive and negative regulation on the yap1 and yap1b, respectively.•Dap-seq revealed that yap1 and yap1b regulated JAK-STAT, prolactin, and steroid signaling pathways.•Verteporfin treatment caused a decrease of yap1/yap1b and a reduction in C. semilaevis growth rate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In animal societies, control over resources and reproduction is often biased towards one sex. Yet, the ecological and evolutionary underpinnings of male-female power asymmetries remain poorly ...understood. We outline a comprehensive framework to quantify and predict the dynamics of male-female power relationships within and across mammalian species. We show that male-female power relationships are more nuanced and flexible than previously acknowledged. We then propose that enhanced reproductive control over when and with whom to mate predicts social empowerment across ecological and evolutionary contexts. The framework explains distinct pathways to sex-biased power: coercion and male-biased dimorphism constitute a co-evolutionary highway to male power, whereas female power emerges through multiple physiological, morphological, behavioural, and socioecological pathways.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Sexual size dimorphism is one of the most striking animal traits, and among terrestrial animals, it is most extreme in certain spider lineages. The most extreme sexual size dimorphism (eSSD) is ...female biased. eSSD itself is probably an epiphenomenon of gendered evolutionary drivers whose strengths and directions are diverse. We demonstrate that eSSD spider clades are aberrant by sampling randomly across all spiders to establish overall averages for female (6.9 mm) and male (5.6 mm) size. At least 16 spider eSSD clades exist. We explore why the literature does not converge on an overall explanation for eSSD and propose an equilibrium model featuring clade- and context-specific drivers of gender size variation. eSSD affects other traits such as sexual cannibalism, genital damage, emasculation, and monogyny with terminal investment. Coevolution with these extreme sexual phenotypes is termed eSSD mating syndrome. Finally, as costs of female gigantism increase with size, eSSD may represent an evolutionary dead end.
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.
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•Brown boobies are good monitors to indicate the presence of mercury.•Despite a reverse sexual dimorphism, Hg concentrations were similar for both sexes.•In blood, Hg concentrations of adults and juveniles were similar due the same diet.•This seabird population had low Hg concentrations, below to the threshold limit.•This is the first study to analyze methylmercury in tissues of a tropical seabird.
Tropical seabird species, with reverse sexual dimorphism had similar Hg concentrations between sexes, while adults showed higher Hg concentrations than juveniles in feathers, but not in blood.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In many animals, body size is correlated with reproductive success. Selection sometimes generates striking differences in body size between males and females (i.e. sexual size dimorphism, SSD). SSD ...is common in spiders (Araneae), and is typically explained by selection for larger, more fecund females and rapidly maturing, and consequently smaller, males. Within a species males and females also often vary in body size. In the false widow spider, Steatoda grossa, females are larger than males and males trade body size for rapid development and early maturation. Moreover, males vary considerably in body size, suggesting that under certain conditions there may be advantages to large size. Here, we tested the role of male body size on mating success under noncompetitive and competitive mating conditions (i.e. male–male competition) in S. grossa. We found that body size did not influence mating success or copulation duration under noncompetitive conditions, but that larger males were more successful at obtaining access to females under competitive mating conditions. Additionally, we found that total copulation duration was significantly lower when a rival male was present. Our results show a large male advantage under male–male competition, which we suggest may contribute to the high variation in male body size observed in S. grossa. We further suggest that the reduced copulation duration observed under competitive mating conditions may have potential ramifications for male and female reproductive success and we discuss how patterns of selection acting on male body size might limit the extent of SSD in this species.
•Male body size is important for mating success in many species.•Steatoda grossa males obtain mating success regardless of body size.•Under competitive conditions, larger males had greater mating success.•Female copulation duration was reduced in the presence of a male competitor.•The results offer insight into male body size evolution and sexual size dimorphism.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract The ‘bigger is better’ hypothesis (BIBH) predicts that fitness increases with body size. Eastern spiny softshell turtles (Apalone spinifera) exhibit sexual size dimorphism (SSD) at maturity, ...and the much larger female body size is attributed to selection favouring greater reproductive output. Hatchlings exhibit sexually dimorphic markings, but hatchling SSD has not been investigated. The BIBH predicts that hatchlings will not exhibit SSD because reproductive benefits to larger, mature females drive size dimorphism at maturity, but selection on hatchlings relates only to survival. We tested this prediction with A. spinifera hatchlings (N = 2630) incubated in controlled conditions to avoid confounding environmental effects on phenotype. Hatchling mass was similar between sexes, suggesting similar nutritional allocation to male and female offspring. Hatchling size (carapace length) was also similar between sexes. Hatchling mass and body size varied among clutches and were positively related to maternal size, suggesting morphological constraints on egg size. Surprisingly, clutch size was related only weakly to maternal size. Taken together, our results suggest that hatchling size in A. spinifera is consistent with the BIBH and that offspring quality increases with maternal age, but that maternal effects drive a large proportion of the variation in clutch size and offspring quality.
Parental care and the evolution of terrestriality in frogs Vági, Balázs; Végvári, Zsolt; Liker, András ...
Proceedings - Royal Society. Biological sciences/Proceedings - Royal Society. Biological Sciences,
04/2019, Volume:
286, Issue:
1900
Journal Article
Peer reviewed
Open access
Frogs and toads (Anura) exhibit some of the most diverse parental strategies in vertebrates. Identifying the evolutionary origins of parenting is fundamental to understanding the relationships ...between sexual selection, social evolution and parental care systems of contemporary Anura. Moreover, parenting has been hypothesized to allow the invasion of terrestrial habitats by the ancestors of terrestrial vertebrates. Using comprehensive phylogenetic analyses of frogs and toads based on data from over 1000 species that represent 46 out of 55 Anura families, we test whether parental care is associated with terrestrial reproduction and several life-history traits. Here, we show that both the duration of care and offspring protection by males and females have coevolved with terrestrial reproduction. Sexual size dimorphism is also related to care, because the large male size relative to female size is associated with increased paternal care. Furthermore, increased egg size and reduced clutch volume are associated with increased care in bivariate but not in multivariate analyses, suggesting that the relationships between care, egg size and clutch volume are mediated by terrestrial reproduction. Taken together, our results suggest that parenting by males and females has coevolved, and complex parenting traits have evolved several times independently in Anura in response to breeding in terrestrial environments.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
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