Testis Asymmetry and Sperm Length inRhacophorus omeimontis

Testis Size Variation and Its Environmental Correlates in Andrew's Toad (Bufo andrewsi)

Reproductive investments influenced by environmental conditions vary extensively among geographically distinct populations. However, investigations of patterns of intraspecific variation in male reproductive investments and the mechanisms shaping this variation in anurans remain scarce. Here, we focused on the variation in testis size in 14 populations of the Andrew's toad Bufo andrewsi, a species with weak dispersal ability but wide distribution in southwestern China, to establish whether male reproductive investment varies on an environmental gradient. Our analysis revealed a significant variation in relative testis size across populations, and a positive correlation between testis size and body condition. We, however, found no geographic trends explaining the variability in the testis size. The relative testis size did not increase with increasing latitude or altitude. We also found no relationship between relative testis size and rainfall, but a negative correlation with the coefficient of variation of temperature, with larger testes under stable environments. These findings suggest that the decreased male reproductive investment of this species may be a consequence of harsher or fluctuating environmental conditions.

Bilateral asymmetry in bullfrog testes and fat bodies: correlations with steroidogenic activity, mast cells number and structural proteins

In seasonal breeders, such as amphibians, testicular functions depend on complex processes that change according to seasonality, including Leydig cell (LC) differentiation and lipid-dependent steroidogenesis, extracellular proteins remodeling and actin-dependent cellular dynamics. Speculating that fat bodies (FB) could support some of these processes in L. catesbeianus, we evaluated bilaterally the FB weights, correlating them to testicular parameters such as weight, testosterone (T) immunoexpression, mast cells (MC) number, vascularization and structural proteins. In an attempt to better understand the testicular asymmetry in amphibians, correlations between these different testicular parameters were also established. Right testes (RT), left testes (LT) and associated FB of bullfrogs were weighed, and testes were processed for light and transmission electron microscopy. Collagen content (COL) and MC number were quantified. T and actin immunoexpressions and vascular areas were measured. Statistical analyses and Pearson's correlation were performed. The LT and its associated FB were heavier than the right ones, and showed intense T and actin immunoexpressions, numerous lipid-rich LC, and greater MC number, COL and vascularization than the RT. Positive correlations were detected between: a) FB and testis weights, b) T immunoexpression and testis and FB weights, c) T and actin immunoexpressions and COL. Otherwise, MC number was inversely correlated to T immunoexpression and COL. In right and left sides, the proportional correlation between T immunoexpression and FB weight suggests that FB-stored lipid amount depends on the steroidogenic demand of its associated testis. Thus, the asymmetry in the testes and FB may be associated, at least in part, to the LC steroidogenic activity, which tends to be more intense in LT than in RT. The results also point to a role of COL and mast cells in the LC differentiation and steroidogenesis. Actin was also greater in LT and correlated with T immunoexpression, indicating that the amount of this structural protein depends on androgenic control. Therefore, the testicular asymmetry in bullfrogs seems to be associated to different morphofunctional processes occurring, bilaterally, at different intensities. In this case, there is a tendency of LT, in association with its FB, to be more active than RT. The findings highlight the FB-testis interplay for the comprehension of reproduction in amphibians.

Variation in testis weight of the Tibetan toad Scutiger boulengeri along a narrow altitudinal gradient

Life-history theory predicts that organisms inhabiting harsh environments such as high altitudes should invest less in reproduction and more in survival. Testis size is associated with the intensity of male-male competition for mating and thus may be treated as an indicator of male reproductive investment. Hence, it may be expected that organisms will reduce their testis size with increasingly harsh environments. Here we test this prediction in a toad species, Scutiger boulengeri, endemic to the Tibetan plateau using data from three populations located at altitudes of 4078, 4276, and 4387 m. Consistent with the prediction, male toads exhibited smaller testes at higher altitudes, despite the relatively narrow altitudinal span. It is likely that cold climates and strong seasonality constrain the ability of high-altitude male toads to allocate more energy into reproduction, thereby leading to small testis size. In addition, the left testis was significantly heavier than the right one and the degree of size asymmetry was unrelated to either altitude or body condition.

Influence of physiological stress on the presence of hypoplasia and fluctuating asymmetry in a medieval population from the village of Sypniewo

This study aims to estimate the levels of physiological stress in the medieval rural population of Sypniewo by evaluating patterns of fluctuating asymmetry (FA) and enamel hypoplasia (EH), and provide information on the influence of physiological stress during the prenatal and perinatal period on early childhood development. Stress is defined as any external or internal condition that challenges homeostasis of an organism. FA is associated with physiological stress occurring mainly during prenatal development and early childhood. The level of FA is thought to reflect the intensity of the stressor(s). EH is caused by physiological stress such as nutritional instability during the first years of life. The studied material consisted of 126 skulls from the village of Sypniewo (Poland). Cranial radiographs were taken in postero-anterior (P-A) and basal views. The images were scanned and calibrated. Measurements of the cranium were used to estimate FA. The presence of EH was assessed using standard anthropological methods The highest levels of FA were observed in the region of the cranial base. EH was observed in 29% of individuals from the rural skeletal series. There was no statistically significant correlation between FA and EH occurrence or between sex and the studied stress indicators.

Population density and structure drive differential investment in pre- and postmating sexual traits in frogs

Sexual selection theory predicts a trade-off between premating (ornaments and armaments) and postmating (testes and ejaculates) sexual traits, assuming that growing and maintaining these traits is costly and that total reproductive investments are limited. The number of males in competition, the reproductive gains from investing in premating sexual traits, and the level of sperm competition are all predicted to influence how males allocate their finite resources to these traits. Yet, empirical examination of these predictions is currently scarce. Here, we studied relative expenditure on pre- and postmating sexual traits among frog species varying in their population density, operational sex ratio, and the number of competing males for each clutch of eggs. We found that the intensifying struggle to monopolize fertilizations as more and more males clasp the same female to fertilize her eggs shifts male reproductive investment toward sperm production and away from male weaponry. This shift, which is mediated by population density and the associated level of male-male competition, likely also explains the trade-off between pre- and postmating sexual traits in our much broader sample of anuran species. Our results highlight the power of such a multilevel approach in resolving the evolution of traits and allocation trade-offs.

Sperm length variations in five species of cypridoidean non-marine ostracods (Crustacea)

Spermatozoa of the ostracod superfamily Cypridoidea include some of the longest in the animal kingdom, but unlike other so-called giant spermatozoa, they are aflagellate, probably evolved only once, and represent an exceptionally old trait. Sperm length variations within cypridoidean species remain poorly known, a lack that hinders the development of hypotheses to explain their length and variation. For this study, the lengths of 500 spermatozoa from each of five species of freshwater cypridoidean ostracods, Candonopsis tenuis (Brady, 1886), Fabaeformiscandona subacuta (Yang, 1982), Heterocypris rotundata (Bronshtein, 1928), Ilyocypris japonica Okubo, 1990, and Notodromas trulla Smith and Kamiya, 2014, were measured, including the lengths of the posterior and anterior regions. No overall pattern in sperm variation was discernible. Length variations between species, between males of the same species, and within individual males varied from low (Candonopsis tenuis) to extraordinarily large (Notodromas trulla and Fabaeformiscandona subacuta). Sperm competition, cryptic female choice, sperm heteromorphism, and testis size are unlikely to explain all of the variations observed. Age structures of the populations sampled might play a role in explaining some intraspecific variation. The differing amounts of variation in sperm characters revealed in this study suggest that multiple evolutionary trends and pressures shape sperm lengths in this superfamily.

Sexual selection impacts brain anatomy in frogs and toads

Natural selection is a major force in the evolution of vertebrate brain size, but the role of sexual selection in brain size evolution remains enigmatic. At least two opposing schools of thought predict a relationship between sexual selection and brain size. Sexual selection should facilitate the evolution of larger brains because better cognitive abilities may aid the competition for mates. However, it may also restrict brain size evolution due to energetic trade‐offs between brain tissue and sexually selected traits. Here, we examined the patterns of selection on brain size and brain anatomy in male anurans (frogs and toads), a group where the strength of sexual selection differs markedly among species, using a phylogenetically controlled generalized least‐squared (PGLS) regression analyses. The analysis revealed that in 43 Chinese anuran species, neither mating system, nor type of courtship, or testes mass was significantly associated with relative brain size. While none of those factors related to the relative size of olfactory nerves, optic tecta, telencephalon, and cerebellum, the olfactory bulbs were relatively larger in monogamous species and those using calls during courtship. Our findings support the mosaic model of brain evolution and suggest that while the investigated aspects of sexual selection do not seem to play a prominent role in the evolution of brain size of anurans, they do impact their brain anatomy.

Altitudinal variation in male reproductive investment in a polyandrous frog species (Hyla gongshanensis jingdongensis)

Competition for fertilization in multi-male group spawning can drive variation in male reproductive investment (i.e., testis mass and sperm size). Inter-population comparisons of variation in energetic availability and allocation along geographical gradients allow insights into the mechanisms shaping the reproductive investments of animals. Although inter-population differences in female reproductive investment (i.e., clutch size and egg size) have been studied extensively across a wide range of taxa, little information on variation in reproductive investment in males is available. Here, we studied altitudinal variation in testis mass and sperm length among three populations in the Jingdong tree frog (Hyla gongshanensis jingdongensis), a polyandrous species, in Yunnan Province in China. The results showed that individuals exhibited smaller testes at higher altitudes while testes mass was positively correlated with body size, body condition and age. Longer sperm length was observed in the middle-altitude population. Moreover, we found that sperm number was positively correlated with testes mass and sperm length. Our correlational findings suggest that environmental constraints at high altitude select for less investment in testes and offspring number.

Evolution of anuran brains: disentangling ecological and phylogenetic sources of variation

Variation in ecological selection pressures has been implicated to explain variation in brain size and architecture in fishes, birds and mammals, but little is known in this respect about amphibians. Likewise, the relative importance of constraint vs. mosaic hypotheses of brain evolution in explaining variation in brain size and architecture remains contentious. Using phylogenetic comparative methods, we studied interspecific variation in brain size and size of different brain parts among 43 Chinese anuran frogs and explored how much of this variation was explainable by variation in ecological factors (viz. habitat type, diet and predation risk). We also evaluated which of the two above-mentioned hypotheses best explains the observed patterns. Although variation in brain size explained on average 80.5% of the variation in size of different brain parts (supporting the constraint hypothesis), none of the three ecological factors were found to explain variation in overall brain size. However, habitat and diet type explained a significant amount of variation in telencephalon size, as well in three composite measures of brain architecture. Likewise, predation risk explained a significant amount of variation in bulbus olfactorius and optic tecta size. Our results show that evolution of anuran brain accommodates features compatible with both constraint (viz. strong allometry among brain parts) and mosaic (viz. independent size changes in response to ecological factors in certain brain parts) models of brain size evolution.

Evidence for neither the compensation hypothesis nor the expensive-tissue hypothesis in Carassius auratus

In many taxa, the left and right testes often differ in size. The compensation hypothesis states that an increase in size of one testis can compensate for a reduced function in the other testis. Moreover, the expensive-tissue hypothesis predicts that an increase in investment of a metabolically costly tissue is offset by decreasing investment in the other metabolically costly tissues. Here we tested these two hypotheses in Carassius auratus, by analysing difference between left and right testes mass, and between brain mass and both gut length and gonad mass (testes mass in males and clutch mass in females). We found no difference between left and right testis mass and no correlations between relative testis size and body measurements. These findings suggest that the left testis cannot serve a compensatory role. Nonetheless, contrary to the predictions of the expensive-tissue hypothesis, brain mass was positively correlated with both gut length and gonad mass within each sex. This positive correlation between brain mass and other organs (gut, gonad and clutch tissues) suggests that organisms may compensate for substantial variation in investment in tissues without sacrificing other expensive tissues.