Social control of male sexual maturation in the swordtail characin, Corynopoma riisei

The presence of adult male Corynopoma riisei was found to inhibit the maturation of juvenile males. Males in a conspecific community tank took longer to mature and did so at increasingly slower rates compared to isolated controls, providing a positive correlation between size and time of maturational onset. The inhibitory effect increased with greater numbers of adult males. The first males to mature did so at accelerated rates, suggesting positive as well as negative control. Tanks in which adult males were removed as soon as maturation was complete showed an intermediate pattern, with no lengthening of the maturational time course but an increase in standard length. Histological examination revealed immature males with lengths greater than the control range; these appear to represent inhibited animals. Both the testes and pituitary gonadotropic zone of these males appeared undeveloped, arguing for inhibition at least at the hypothalamic level. This phenomenon has also been described in poeciliids The presence of a similar complex mechanism in two distant groups of fishes suggests convergent evolution. It also suggests that this phenomenon may be physiologically possible for a wide range of fish species.     

Environmental correlates of diet in the swordtail characin (Corynopoma riisei, gill)

In the sexually dimorphic swordtail characin (Corynopoma riisei, Gill), males are equipped with an opercular flag-ornament that has been suggested to function as a food-mimic since females bite at the ornament during courtship. However, virtually nothing is known about the diet in wild populations of this species. In this study, we first investigated composition of and variation in the diet of C. riisei across 18 different populations in Trinidad, using gut content analyses. We then related variation in gut content to habitat features of populations to investigate the potential link between environmental conditions and prey utilization. Our results showed that the dominating food type in the gut was various terrestrial invertebrates, both adults and larvae, but we also document substantial variation in prey types across populations. Furthermore, a canonical correlation analysis revealed a relationship between environmental characteristics and diet: populations from wider and more rapidly flowing streams with more canopy cover tended to have a diet based more on ants and mosquitoes while populations from narrow and slow flowing streams with little canopy cover tended to have a diet based more on springtails, mites and mayfly larvae. Our results add novel information on the ecology of this interesting fish and suggest the possibility of local adaptation reflecting differences in prey availability across natural populations.     

Population differentiation in the swordtail characin (Corynopoma riisei ): a role for sensory drive?

Sensory drive, where the efficacy of a sexual signal depends on the environment in which it is employed, is a potential mechanism behind divergent evolution of secondary sexual traits. Male swordtail characins are equipped with a narrow and transparent extension of the gill cover with a flag‐like structure at its tip. This opercular flag mimics a prey item and is employed by males as a ‘lure’ to attract the attention of females during mating attempts. We conducted a study of genetic and morphological differentiation across swordtail characin populations throughout their native range in Trinidad. The morphology of the opercular flag varied across populations and several aspects of this variation match the predicted hallmarks of sensory drive. First, morphological differentiation of the flag across populations was unrelated to genetic similarity at neutral genetic markers. Second, the shape of the flag covaried with those aspects of body shape that should reflect adaptation to different feeding regimes. Third, and most importantly, the shape of the flag covaried across populations with those environmental characteristics that should most closely reflect differences in local prey abundance. Overall, our results are consistent with a scenario where the evolution of this male sexual signal tracks food‐related shifts in female sensory biases across populations, thus providing at least provisional support for a role for sensory drive in population differentiation.     

A polymorphism in female preference for a polymorphic male trait in the swordtail fish Xiphophorus cortezi

Xiphophorus cortezi males are polymorphic for the pigment pattern vertical bars. In this study, we determined whether X. cortezi females are polymorphic in their preference for this trait by examining both within- and between-individual variation in female preference. There was significantly more variation in female preference within than between individuals using both video animations and live males as stimuli; repeatability measures were 0.86 and 0.5, respectively. Some females had a strong preference for males with bars, some for males without bars, and some had either a weak preference or no preference at all. We also found a significant difference in the strength of preference for bars between females with and without bars, suggesting the potential for a genetic correlation between preference and trait. Finally, we examined female preference for bar symmetry in the same females tested for preference for bars. We detected a significant preference for bar symmetry in the population of females as a whole, and a positive relationship between the strength of this preference and a preference for the presence/absence of bars among the subset of females that preferred ‘no bars’. We discuss these results in light the possibility that these two preferences are interrelated. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Proximate basis of the covariation between a melanin-based female ornament and offspring quality

In contradiction to sexual selection theory, several studies showed that although the expression of melanin-based ornaments is usually under strong genetic control and weakly sensitive to the environment and body condition, they can signal individual quality. Covariation between a melanin-based ornament and phenotypic quality may result from pleiotropic effects of genes involved in the production of melanin pigments. Two categories of genes responsible for variation in melanin production may be relevant, namely those that trigger melanin production (yes or no response) and those that determine the amount of pigments produced. To investigate which of these two hypotheses is the most likely, I reanalysed data collected from barn owls (Tyto alba). The underparts of this bird vary from immaculate to heavily marked with black spots of varying size. Published cross-fostering experiments have shown that the proportion of the plumage surface covered with black spots, a eumelanin composite trait so-called plumage spottiness, in females positively covaries with offspring humoral immunocompetence, and negatively with offspring parasite resistance (i.e. the ability to reduce fecundity of ectoparasites) and fluctuating asymmetry of wing feathers. However, it is unclear which component of plumage spottiness causes these relationships, namely genes responsible for variation in number of spots or in spot diameter. Number of spots reflects variation in the expression of genes triggering the switch from no eumelanin production to production, whereas spot diameter reflects variation in the expression of genes determining the amount of eumelanin produced per spot. In the present study, multiple regression analyses, performed on the same data sets, showed that humoral immunocompetence, parasite resistance and wing fluctuating asymmetry of cross-fostered offspring covary with spot diameter measured in their genetic mother, but not with number of spots. This suggests that genes responsible for variation in the quantity of eumelanin produced per spot are responsible for covariation between a melanin ornament and individual attributes. In contrast, genes responsible for variation in number of black spots may not play a significant role. Covariation between a eumelanin female trait and offspring quality may therefore be due to an indirect effect of melanin production.     

Genetic architecture of sensory exploitation: QTL mapping of female and male receiver traits in an acoustic moth

The evolution of extravagant sexual traits by sensory exploitation occurs if males incidentally evolve features that stimulate females owing to a pre‐existing environmental response that arose in the context of natural selection. The sensory exploitation process is thus expected to leave a specific genetic imprint, a pleiotropic control of the original environmental response and the novel sexual response in females. However, females may be subsequently selected to improve their discrimination of environmental and sexual stimuli. Accordingly, responses may have diverged and the original genetic architecture may have been modified. These possibilities may be considered by studying the genetic architecture of responses to male signals and to the environmental stimuli that were purportedly ‘exploited’ by those signals. However, no previous study has addressed the genetic control of sensory exploitation. We investigated this question in an acoustic pyralid moth, Achroia grisella, in which a male ultrasonic song attracts females and perception of ultrasound likely arose in the context of detecting predatory bats. We examined the genetic architecture of female response to bat echolocation signals and to male song via a cartographic study of quantitative trait loci (QTL) influencing these receiver traits. We found several QTL for both traits, but none of them were colocalized on the same chromosomes. These results indicate that – to the extent to which male A. grisella song originated by the process of sensory exploitation – some modification of the female responses occurred since the origin of the male signal.     

Secondary reduction of preference for the sword ornament in the pygmy swordtail Xiphophorus nigrensis (Pisces: Poeciliidae)

Female mating preferences can be secondarily lost for a number of reasons. We examined the preference of female pygmy swordtails, Xiphophorus nigrensis, for the sword, a conspicuous extension of the caudal fin in some males. Females failed to show a preference for conspecific males with swords when presented with live males naturally varying in sword length, with live males of manipulated sword length, and with synthetic animations of males expressing natural variation in sword length. Females showed a significant bias against swords when presented with synthetic animations bearing supernormal sword characteristics. The reduced preference for swords, relative to closely related fish, may result from an increase in the cost of choice due to predation risk, selection against mating with heterospecifics, or changes in the spatial and contrast properties of the conspecific signal.     

Correlation between male and female reproduction in the subdioecious herb Astilbe biternata (Saxifragaceae)

Genotypic trade-offs between male and female reproduction are commonly assumed in theoretical studies of the evolution of gender specialization. Although these trade-offs are supported by higher seed production of females than hermaphrodites in natural populations of gynodioecious species, comparisons between male and female reproductive allocation among hermaphrodite individuals under controlled conditions are rare. We assessed phenotypic and genotypic correlations between stamen and fruit production in fruiting males of the near-dioecious herb Astilbe biternata. In the field, we found a significant negative phenotypic correlation between stamen production and fruit production within individuals that produced both stamens and fruit as well as higher fruit set in females than fruiting males. The negative correlation between fruit and stamen production that was observed in the field was also apparent across clonally propagated genotypes. These results suggest that negative genetic correlations between male and female reproduction may limit the independent evolution of fruit and stamen production in A. biternata.     

Evaluating a predator–prey interaction in the field: the interaction between beetle larvae (predator) and tadpoles (prey)

The larval amphibian community of temporary pond ecosystems has served as a model for studies in community ecology, with a majority of this work being conducted in mesocosms. Recent research has suggested that mesocosms may overestimate ecological effects; therefore, experimental studies conducted under field conditions are required to gauge the results of mesocosm studies. To assess a species interaction under more natural conditions, we conducted a series of field experiments examining the predator–prey interaction between beetle larvae ( Dytiscus sp.; predator) and larval wood frogs Rana sylvatica (prey) in central Pennsylvania, USA. Quantitative sampling of woodland ponds indicated that beetle larvae of the genus Dytiscus were the most common predator of tadpoles. In a field enclosure experiment, dytiscids were effective predators of tadpoles in the pond environment. Moreover, tadpoles avoided areas in a pond containing caged dytiscids, demonstrating that tadpoles recognize the chemical stimuli of predators in complex environments. The results of this study are consistent with data from prior laboratory and mesocosm studies and suggest that these venues can produce reliable interpretations of predator–prey dynamics in this community.     

A test for negative frequency-dependent mating success as a function of male colour pattern in the bluefin killifish

Rare male mating advantage (a form of negative frequency dependence) is frequently proposed as a mechanism for the maintenance of genetic variation within populations. This hypothesis is attractive for systems with pronounced male colour polymorphism because it can maintain particularly high levels of variation. We tested for negative frequency-dependent mating success between yellow and red male colour patterns in bluefin killifish, Lucania goodei . Lucania goodei populations harbour substantial colour pattern polymorphism, and a large proportion of this variation has a genetic basis. We established outdoor mesocosms with red and yellow males in three different ratios: yellow rare (one yellow ♂ : five red ♂), even (three yellow ♂ : three red ♂), and red rare (five yellow ♂ : one red ♂). We obtained eggs and used microsatellites to determine paternity. By contrast to expectations, we found no support for a rare male mating advantage. Red males had slightly higher spawning success than yellow males, particularly in replicates with large clutches and when red males were rare. However, yellow males did not have higher mating success when rare. We discuss alternative mechanisms for the maintenance of the polymorphism as well as the potential reasons for the lack of a rare male mating advantage.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 489–500.     

The function of female and male ornaments in the Inca Tern: evidence for links between ornament expression and both adult condition and reproductive performance

Inca Terns Larosterna inca are medium-size seabirds that breed along the Peruvian and Chilean coast. They are monogamous and both sexes incubate and contribute to chick provisioning. The sexes are similar in appearance and have elaborate ornaments, including a long white moustache of feathers and fleshy yellow wattles. In this paper we report the differences in ornamentation between sexes and examine whether the trait predicts body condition, reproductive performance or chick quality in either sex. The ornaments were similar in size and coloration between the sexes, except for the wattle length, the difference in which can be due to greater head length in males. Moustache length was the most reliable signal of body condition in both sexes. Moreover, there was a significant relationship between the moustache length and reproductive category of adults (non-breeder, unsuccessful breeder, or one or two chicks fledged). Both asymptotic chick body mass and the T-cell mediated response of chicks (a measure of immunocompetence) were related to the moustache length of male and female adults. These results provide support for the role of ornaments in mutual signalling of condition in this species. Female and male ornaments predict body condition, reproductive performance and chick quality, as predicted by sexual selection models.     

Contrasting patterns of selection on the size and coloration of a female plumage ornament in common yellowthroats

Females often possess ornaments that appear smaller and duller than homologous traits in males. These ornaments may arise as nonfunctional by‐products of sexual selection in males and cause negative viability or fecundity selection in females in proportion to the cost of their production and maintenance. Alternatively, female ornaments may function as signals of quality that are maintained by sexual or social selection. In a 4‐year study of 83 female common yellowthroats (Geothlypis trichas) and their 222 young, we found strong viability and fecundity selection on the yellow bib, a carotenoid‐based plumage ornament that is a target of sexual selection in males. Females with larger bibs were older, larger and more fecund than females with smaller bibs. However, bib size positively covaried with bib total brightness and carotenoid chroma, aspects of bib coloration that were under negative viability and fecundity selection. Females with more colourful bibs laid fewer eggs in their first clutch, were more likely to suffer total brood loss due to predation and were less likely to return to the study area. Selection against bib coloration limits the value of bib size as a quality indicator in females and may constrain the elaboration of bib attributes in males.     

雌雄子午沙鼠的认知行为及其神经内分泌水平的差异

本研究通过对雌雄子午沙鼠进行新物体识别和社会认知实验,运用免疫组化方法检测其相关脑区合成催产素（OT）、加压素（AVP）和多巴胺（DA）能的神经元数量,采用酶联免疫试验（ELISA）方法检测了其血清中OT、AVP的水平,探究了雌雄子午沙鼠的两性认知差异及其神经内分泌水平的差异。结果表明,雌雄子午沙鼠对新物体的探究时间均要显著高于旧物体,雌雄子午沙鼠的辨别指数无显著差异（P＞0.05）;雄性子午沙鼠随着探究次数的增加对重复刺激鼠a的探究时间不断减少,对陌生刺激鼠b的探究时间显著高于刺激鼠a（P＜0.05）;雌性子午沙鼠没有此趋势。雄性子午沙鼠OT能神经元数量在下丘脑室旁核(PVN)和视上核(SON)均要显著少于雌性（P＜0.05）;雄性个体DA能神经元数量在黑质显著高于雌性（P＜0.01）;然而雄性个体DA能神经元数量在腹侧被盖区显著少于雌性（P＜0.01）;雌雄子午沙鼠血清OT、AVP水平均无显著差异。综上所述,雌雄子午沙鼠对新物体的识别能力无显著差异,然而雄性子午沙鼠的社会认知能力强于雌性。在神经内分泌水平上,雌雄子午沙鼠PVN和SON中OT能神经元数量、黑质和腹侧背盖区的DA能神经元数量均呈现出了两性差异。     

Discrimination by male ring-tailed Lemurs (Lemur catta) between the scent marks of male and those of female conspecifics

Olfaction plays an important role in the social communication of all prosimians. (The experiment reported in this paper forms part of an intensive chemobehavioral study of olfaction in Lemur catta (ring-tailed lemur) being carried out in this laboratory.) Five male Lemur cattawere tested on their behavioral responses to paired scent stimuli. Responses measured were (1) total investigation time, (2) arm-marking, (3) ABO/BO rubbing, and (4) flehmen. Males showed a strong discrimination between the scent stimuli,giving higher levels of response to female scent on measures 1, 3, and 4. This response suggests an olfactory-related preference by males for female scent under controlled conditions. This preference may be a consequence of the females’ dominance over males and the brevity of estrus in L. catta,both of which would favor such choice behavior.     

Experimental manipulation reveals differential effects of colour pattern on survival in male and female pygmy grasshoppers

Populations of pygmy grasshoppers, Tetrix subulata, exhibit genetically coded discontinuous variation in colour pattern. To determine whether the dynamics of this polymorphism is likely to be affected by selective processes, rather than by stochastic events, we experimentally manipulated colour patterns of free-ranging grasshoppers and then calculated and controlled for differences in capture probabilities between categories of individuals before estimating and testing for differences in survival using mark–recapture data and program SURGE . We found that paint treatment had a significant effect on survival, and that the relationship between colour pattern and survival was different in males and females. Our analyses also revealed significant differences between sexes in relative frequencies of natural colour morphs, body size, activity pattern, dispersal distance and microhabitat use. These findings accord with the hypothesis that colour pattern and behaviour jointly determine susceptibility to visual predators. Our data enable us to reject the null-hypothesis that colour pattern is a selectively neutral character and that the polymorphism is maintained solely by stochastic processes, such as random genetic drift and founder events. Indeed, the effect of dorsal coloration on survival, together with associations between colour pattern and many biologically important traits (body size, behaviour, thermal capacity, physiology and reproductive performance), suggests that colour pattern is likely to significantly influence individual fitness, and that the polymorphism must be maintained by some active process, such as spatially variable selection in combination with gene flow. The possible role of colour polymorphism as an intermediate stage in the evolution of sexual dichromatism in animals is discussed.     

Behavioural differences between male and female replacement reproductives in Kalotermes flavicollis (Isoptera, Kalotermitidae)

Summary: An ethogram type study was performed on representative colonies of Kalotermes flavicollis to investigate the behavioural repertoires of replacement king and queen. Our observations suggested a sex-based behavioural specialisation in the two reproductives, affecting colony organisation and equilibrium. Interesting differences were detected in overall activity of the two reproductives, with the male showing the greatest frequency of movements in the nest, vibratory acts, and the highest rate and range of social contacts. In addition to his importance for periodical insemination of the queen, the king might also play a basic role in the social structure and dynamic development of the colony, as a "mediator" in social interactions between the queen and the other colony members.