Male-male interactions and their influence on the mating behavior and success in the fountain darter, <Emphasis Type="Italic">Etheostoma fonticola</Emphasis>

Behavioral interactions between individuals of the same sex can affect the outcome of intersexual selection. For this reason, intrasexual selection is oftentimes examined independently from intersexual selection in studies aimed at understanding mating behaviors. However, a more complete understanding of sexual selection effects within a population can only come from exploring both intrasexual and intersexual selection and the potential interactions between the levels of selection. Association preferences in male and female Etheostoma fonticola do not reveal a size preference for same sex or opposite-sex individuals. However, male-male interactions may influence female choice in E. fonticola. We examined whether male E. fonticola that differ in body size exhibit differences in agonistic behaviors and mating success. Larger males do exhibit higher rates of aggressive behaviors and smaller males, in turn, exhibit more defensive behaviors. However, differences between larger and smaller males in male-male interactions did not translate into differences in spawning success. These results suggest that male size influences dominance relationships in E. fonticola but not mating success. There were also no differences between large and small males in mating attempts, which could be an outcome of the year-round breeding season found in this species, females laying eggs singly, or males fertilizing eggs individually.     

Sex and Weapons: Contrasting Sexual Dimorphisms in Weaponry and Aggression in Snapping Shrimp

Sexual dimorphisms in weaponry and aggression are common in species in which one sex (usually males) competes for access to mates or resources necessary for reproduction – sexually dimorphic weaponry and aggression, in other words, are frequently the result of intrasexual selection. In snapping shrimp, the major chela (snapping claw) can be a deadly weapon, and males of many species have larger chelae than females, a pattern readily interpreted as resulting from intrasexual selection. Thus, males might be expected to show more sex‐specific aggression than females, and be more aggressive overall. We tested these predictions in two species of snapping shrimp in a territorial defense context. Neither of these predictions was supported: in both species, females, but not males, engaged in sex‐specific aggression and females were more aggressive than males overall. These contrasting sexual dimorphisms – larger weaponry in males but higher aggression in females – highlight the importance of considering the function of weaponry and aggression in contexts other than direct competitions over mates. In addition, species differences in the degree of sexual dimorphism in chela size were due to differences in female, not male, chela size, and the species with greater sexual dimorphism in weaponry was significantly less aggressive overall; also, while paired and solitary males did not differ in residual chela size, for the species with greater sexual dimorphism, females carrying embryos had smaller residual chela sizes. These results suggest that understanding the sexual dimorphisms in weaponry and aggression in snapping shrimp requires understanding the relative costs and benefits of both in females as well as males.     

Monogamous mating system and sexuality in the gobiid fish, <Emphasis Type="Italic">Trimma marinae</Emphasis> (Actinopterygii: Gobiidae)

The mating system and sexuality of the gobiid fish Trimma marinae were investigated in aquaria and by gonadal histological examination. The male to female sex ratio in the study aggregation was female biased (14:27), and females were larger than males. T. marinae were monogamous because they established continuous pairs and spawned repeatedly with the same individuals. Observations of aggressive behavior suggested that the monogamous mating system resulted from female mate guarding. We also performed a rearing experiment to test whether sex change occurs in this species. None of the males or females reared separately in aquaria for 63 days changed sex. Additionally, gonadal histology revealed that mature fish had unisexual gonads (testis or ovary). These results strongly suggest that T. marinae is gonochoristic. However, immature fish had a bisexual gonadal structure, indicating juvenile hermaphroditism.     

Function of nuchal humps of a cichlid fish from Lake Tanganyika: inferences from morphological data

Nuchal humps occur in various fish groups, but their functions are rarely studied. Both sexes of Cyphotilapia gibberosa, a cichlid fish endemic to Lake Tanganyika, possess nuchal humps. This study morphologically analysed the humps of this species to assess the primary factors responsible for hump development. Semi-landmarks showed that the size of male humps positively correlated with body condition, and thicknesses of hypodermises implied that the humps were larger in males than in females. These facts suggest that sexual selection on male humps is intense. Semi-landmarks showed that the humps were less prominent in females than in males, and that the transformation of nuchal humps with growth (becoming more prominent) ceased at medium body size in females. These facts suggest that sex recognition likely plays a role in the evolution of the uniform humps of large females, because, according to this hypothesis, a morphologically moderate hump may be favoured. If male humps also function as a sex recognition trait, the transformation of nuchal humps is expected to cease at a certain body size, as did female humps. However, the male humps became continuously more prominent from the smallest to the largest individuals examined. The body size at which hump transformation stops or at which extreme hump shape interferes with sex recognition may be outside of the size range of the present samples. A prominent nuchal hump may also function as a species recognition trait, because sympatric cichlid species do not develop nuchal humps as prominent as this species. In short, the present morphological analyses do not contradict the hypotheses that C. gibberosa individuals recognise conspecifics and their sex from the shapes of the nuchal humps, and that females prefer males with larger humps.     

Aggression in harlequin frogs: male-male competition and a possible conflict of interest between the sexes

Long-term field observations and experimental manipulations were made on a population of harlequin frogs, Atelopus varius, in Costa Rica to document seasonality of intra- and intersexual aggression, determine the function of aggression, and identify the factors that influence success in aggressive encounters. Both males and females defended portions of their home range and exhibited site fidelity. Males were more aggressive towards other males during the pre-breeding and breeding seasons, whereas females were more aggressive towards other females during the post-breeding season. For up to several months prior to oviposition, males attempted to amplex (clasp) females without courtship behaviour, while females chased males from their territories and attempted to dislodge males that amplexed them. In staged encounters the winner was usually the apparent resident, regardless of body size. Frogs from a high-density population were more aggressive than individuals from a low-density population. Subadult males were as aggressive and as likely to win encounters as adult males. The function of aggression seemed to be related to the bizarre reproductives behaviour observed in these frogs. There seemed to be male-male competition for mates, as the operational sex ratio strongly favoured males, oviposition was asynchronous, and amplexus lasted for at least several weeks. Female-female aggression may have been related to defence of foraging or shelter sites, but aggression towards males was likely to be an attempt to thwart unwanted amplexus.     

The role of sex ratios and resource availability on the pre-mating behavior of a monogamous fish

Convict cichlid fish (Archocentrus nigrofasciatus) are one of the few monogamous species where the female appears more colorful than the male. We examined whether this sexual dimorphism was reflected in a female-biased actual sex ratio (ASR) and whether convict cichlid females would exhibit behavioral traits typified in monogamous males when they possessed the extravagant colors and/or morphology. Our field observations revealed that females are marginally, but not significantly, more abundant than males but they did initiate more intersexual social interactions (i.e. approach behavior) than males. They also showed more intrasexual aggression. Furthermore, males more commonly chased females rather than vice versa. Our laboratory experiment also indicated that differences in intrasexual aggression were not related to differences in the ASR but did appear with the addition of a breeding site. Thus, while intrasexual competition was more frequently observed between females in the field it was probably related to the availability of breeding sites rather than our estimates of the ASR.     

Intraspecific aggression in rosyside dace, a drift-feeding stream cyprinid

Individual rosyside dace Clinostomus funduloides in a semi-natural, artificial stream displayed substantial differences in their aggressiveness and could be classified as: (1) non-aggressive (NA, 18 of 30 rosyside dace), (2) moderately aggressive (MA, 9 of 30) and (3) highly aggressive (HA, 3 of 30). Rosyside dace groups, however, did not exhibit linear dominance hierarchies and fish size was only weakly correlated with the number of aggressive acts performed per individual. Small rosyside dace (<56 mm L_F) were always non-aggressive, but larger fish were present in all three aggression classes. The difference in size between the contestants was significantly, although not very strongly, correlated with the probability of winning an agonistic interaction (r ²=0·39). Aggressive rosyside dace may have ultimately gained higher fitness than less aggressive ones. HA individuals occupied the upstream-most position within foraging groups significantly more often than other rosyside dace. This location should be the most profitable one because its occupant will be the first to encounter prey. HA rosyside dace also occupied significantly higher focal velocities that were closer to energetic optima than MA and NA ones. They also had greater foraging rates and were less solitary than less aggressive fish, but these differences only were significant at the P=0·066 and P=0·081 level, respectively. Finally, HA fish performed significantly more aggressive acts and feedings backwards than other individuals. Despite these differences, the effects of intraspecific aggression in rosyside dace appeared less substantial than those that have been observed in stream salmonids.     

Comparison of age and growth performance of diploid and tetraploid loach <Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis> in the Yangtze River basin,China

Diploids and tetraploids of the cyprinid loach Misgurnus anguillicaudatus coexist in many natural habitats in Asia. However, little is known about the biological and ecological differences between these two ploidy forms. We examined age, body size and growth rates of fish in a mixed ploidy population of M. anguillicaudatus in the Yangtze River basin in China. The sex ratios of both diploid and tetraploid M. anguillicaudatus were highly skewed toward females, who tended to be larger than males. The age distributions of the collected specimens clearly indicated that tetraploids lived longer than diploids. For example, we found a substantial number of tetraploids that were 5+ years old, while the oldest diploids were 4+ years old. Tetraploids were also longer and heavier than diploids for both sexes. Using the empirical body size and age data, we inferred the growth patterns of these fish with the von Bertalanffy growth function. The estimated asymptotic body lengths (L _∞) indicated that tetraploids could indeed achieve larger body sizes than diploids. This difference was partially due to the increased growth rate, as demonstrated by lower growth coefficient (K) and higher growth performance index (φ’). In sum, we show that tetraploid M. anguillicaudatus exhibited significantly increased longevity and superior growth performance compared to diploids. These differences may contribute to the ecological competitiveness of tetraploid M. anguillicaudatus, thus enabling them to coexist with diploids in certain ecological settings.     

Sex-Specific Aggression and Antipredator Behaviour in Young Brown Trout

Sex differences in adult behaviour are often interpreted as consequences of sexual selection and/or different reproductive roles in males and females. Sex-specific juvenile behaviour, however, has received less attention. Adult brown trout males are more aggressive than females during spawning and juvenile aggression may be genetically correlated with adult aggression in fish. We therefore tested the prediction that immature brown trout males are more aggressive and bolder than immature females. Because previous work has suggested that precocious maturation increases dominance in salmonids, we included precocious males in the study to test the prediction that early sexual maturation increase male aggression and boldness. Aggression and dominance relations were estimated in dyadic contests, whereas boldness was measured as a response to simulated predation risk using a model heron. Independent of maturity state, males initiated more than twice as many agonistic interactions as females in intersexual contests. However, males were not significantly more likely to win these contests than females. The response to a first predator attack did not differ between sex categories, but males reacted less to a second predator attack than females. Sexual maturity did not affect the antipredator response in males. Since there is no evidence from field studies that stream-living immature male and female salmonids differ in growth rate, it appears unlikely that the sex differences demonstrated are behavioural consequences of sex-specific investment in growth. It seems more likely that sex-specific behaviour arises as a correlated response to sexually selected gene actions promoting differential behaviour in adult males and females during reproduction. Alternatively, sex differences may develop gradually during juvenile life, because a gradual developmental program should be less costly than a sudden behavioural change at the onset of sexual maturity.     

Weaponry,size, and sex ratio affect spatial distribution within small and large groups of the maritime earwig (Anisolabis maritima)

Dispersion patterns within a group can reveal important aspects about social interactions and sexual selection within a species. We examined the distribution patterns of the maritime earwig (Anisolabis maritima), an insect well suited for studies of aggression, sociality, and sexual selection since both sexes live in close proximity and possess weaponry in the form of sexually dimorphic pincers. To examine intra‐ and intersexual interactions within small groups, we conducted trials with three earwigs with limited access to shelters. In single‐sex trios, we found that both males and females exhibited strong size‐based intrasexual aggression, as larger individuals were less likely to be excluded from shelters; however, males were more likely to cohabitate than females. In mixed‐sex trios, we found that both males and females preferred smaller opposite‐sex partners, and cohabitation patterns indicate that both sex‐ and size‐based differences in aggression can influence overall spatial distribution. We also examined larger single‐sex and mixed‐sex groups of 18 earwigs to determine whether they had random, uniform, or clumped distributions. Similar to previous field observations, males tended to form aggregations, whereas females were distributed uniformly, a pattern indicative of territoriality. Mixed‐sex groups, on the other hand, were uniform during nocturnal periods of high activity but then become clumped after settling into more stable daytime positions. Overall, our results suggest that females have high levels of aggression regardless of the social context, whereas males alter their aggressive behavior in the presence of females.     

Sexual dimorphism and dichromatism in the cyprinid fish <Emphasis Type="Italic">Puntius titteya</Emphasis>

We documented sexual dimorphism and dichromatism in the cyprinid fish Puntius titteya. We observed no sexual difference in body size, although males had longer fins than females. Male body coloration was redder and exhibited a higher saturation than that of females. However, in females, coloration in the cheek (around the gill cover) was near red and exhibited high saturation compared to coloration of the abdomen. These results clearly indicate sexual dimorphism in fin size and dichromatism in P. titteya, which suggests that this species has a high potential use as a model for studying sexual selection.     

Synchrony during aggression in adult male Atlantic spotted dolphins <Emphasis Type="Italic">(Stenella frontalis)</Emphasis>

Synchrony among Atlantic spotted dolphins (Stenella frontalis) is crucial for successfully overcoming bottlenose dolphins (Tursiops truncatus) during interspecies aggression (Cusick and Herzing 2014). The present study examined synchrony in adult Atlantic spotted dolphins during aggressive encounters with bottlenose dolphins. Across group size, aggressive behaviors increased preceding synchrony, peaked during synchrony, and decreased dramatically after synchrony. Although smaller groups (< 10 dolphins) became synchronous more frequently than larger groups (> 10 dolphins), larger groups remained synchronous longer; however, smaller groups exhibited greater aggressive behaviors during synchrony, suggesting that additional aggressive behaviors may be necessary to compensate for the smaller group size, whereas larger groups may be able to rely on synchrony with less aggression. Disorganized squawk bouts synchronized as physical synchrony began, but only if coupled with escalating aggression.     

Sex-biased aggression and male-only care at sea in Brünnich's Guillemots Uria lomvia and Razorbills Alca torda

In several groups in the order Charadriformes, biparental care is followed by a period of male‐only care. Several hypotheses attempting to explain extended male parental care in shorebirds do not fit the Alcini. In a previous study of Brünnich’s Guillemots Uria lomvia and Razorbills Alca torda, we did not find support for female‐biased parental effort at the breeding site that would lead to males being in better condition to care for chicks at sea. However, in both species, males spent more off‐duty time at the breeding site than females, suggesting greater involvement in the defence of egg or chick, breeding site and mate. We predicted that there would be a male bias in size and aggressive behaviour associated with parental roles. To test this, body size and aggression of attending male and female Brünnich’s Guillemots and Razorbills were measured during incubation and brooding on the Gannet Islands, Labrador. Parental aggression was measured using natural observations of all agonistic interactions and, in Razorbills only, in situ responses to presentations of a predator model. In both species, males were significantly larger than females in culmen and gape length. Guillemot males initiated agonistic interactions more frequently than females during incubation. In contrast, female Guillemots were subjected to aggression more frequently than males and as a result were involved in more fights. In addition, the few chicks that were seen to die were being attended by single females. During the brooding period, Razorbill males responded aggressively to intruders more frequently than females, made more aggressive responses than females, and responded aggressively more frequently and more intensely than females to a predator model. In both species there was a similar male bias in morphology and behaviour that is consistent with male parents being more capable of protecting their chick, a probable advantage to chick survival during the uniparental care phase of some Charadriformes.     

Growth or reproduction: Intrasexual competition in a colonial damselfishStegastes nigricans

Intrasexual competition within colonies of the damselfishStegastes nigricans was investigated. Both males and females held individual territories, and these territories were adjacently distributed, forming distinct conspecific colonies with different size compositions. In both large and small colonies, only relatively large individuals participated in reproduction. Breeding males and females left their territories to court, spawn and aggregate more frequently than non-breeders of the same colonies. Breeders were less frequently attacked by other fish during these excursions than were non-breeders. Most attacks were conducted by breeders of the same sex. This intrasexual aggression may suppress the reproduction of non-breeders at least in large colonies. Non-breeders in large colonies had smaller gonads than breeders of both large and small colonies, but they grew faster than breeders of the same body size in small colonies. This suggests that non-breeders in large colonies allocate energy to growth in order to be reproductively competitive in the future, although only a few of them remained in the same colonies upon maturity. Colony size thus has an effect on the reproductive life histories of individual damselfish.     

`Little Chipmunk' Syndrome? Male Body Size and Dominance in Captive Yellow‐Pine Chipmunks (Tamias amoenus)

In mammals, large males are often assumed to have higher mating success because they have greater success at contest competition. This relationship is often used to explain the prevalence of male-biased sexual size dimorphism in mammals. However, in many small vertebrates, large individuals are not always dominant. Using staged dyadic encounters, we examined the relationship between male body size and social dominance in captive male yellow-pine chipmunks ( Tamias amoenus ), a species with female-biased sexual size dimorphism. The yellow-pine chipmunk has a mating system in which males participate in mating chases and dominant males may have an advantage in acquiring matings with oestrous females. Captive male chipmunks were aggressive in only 28% of 144 paired encounters; however, several lines of evidence indicated that smaller chipmunks were dominant over large chipmunks: (1) small males were dominant in more dyads than large males; (2) within dyads, dominant males were smaller than subordinate males; and (3) small males performed more aggressive behaviour than large males. These results are not consistent with the prediction that large males are typically dominant. If large chipmunks are able to gain matings with females because of qualities other than dominance (such as the ability to successfully find and/or chase receptive females), then the costs of aggression to large chipmunks may outweigh any potential benefits. Small males, but not large males, may improve their mating success by being aggressive.     

Multi-male group and bidirectional sex change in the gobiid fish, <Emphasis Type="Italic">Trimma caudomaculatum</Emphasis>

The gobiid fish, Trimma caudomaculatum, lives in groups. We investigated group structure, mating system and bidirectional sex change of this species. Four groups examined contained more than two males. The males were significantly larger than the females. By the observations in aquarium, the males occupied a nest and the females visited the nest for spawning. While there was no specific pair bond, the males mated with multiple females. Hence, this species establishes multi-male groups. In the experiments, four larger females had changed sex to male among 25 females. The smallest male changed to female in the group of four males.     

Sleeping and Ranging Behavior of the Sambirano Mouse Lemur, <Emphasis Type="Italic">Microcebus sambiranensis</Emphasis>

Primates require secure sleeping sites for periods of rest, but despite their importance, the characteristics of desired sleeping sites are poorly known. Here we investigated the sleeping ecology of a radio-collared population of the Sambirano mouse lemur, Microcebus sambiranensis, during the nonreproductive season in the Anabohazo forest, northwestern Madagascar. We also investigated their ranging behavior and examined the spatial distribution of sleeping sites within the home ranges of the collared individuals. We took measurements of the sleeping tree’s physical characteristics and recorded the number of collared individuals using each sleeping site. We found that M. sambiranensis generally use foliage sleeping sites more frequently than tree holes and individuals slept more frequently in densely foliated trees than in sparsely foliated trees, often alone. We observed no significant differences in home range size or nightly travel distance between males and females; however, home ranges were smaller than those described for other mouse lemur species. Finally, we found that M. sambiranensis sleep peripherally and forage centrally within their home ranges, a behavior not previously described for mouse lemurs. Our results indicate profound differences in the social organization between M. sambiranensis and other mouse lemur species described in the literature, suggesting species-specificity in mouse lemur ecology. Understanding the sleeping ecology and ranging behavior of mouse lemurs is of great importance to their conservation, as these data facilitate the planning of long-term reforestation, habitat management, and population assessment.     

Aggression and dominance in matched groups of subadult Icelandic horses (<Emphasis Type="Italic">Equus caballus</Emphasis>)

We studied sex differences in the nature of aggression and dominance behaviour in two newly formed groups of 1-year-old Icelandic horses. One herd contained nine geldings, the other nine mares. The groups were matched with regard to dominance-determining traits such as age, weaning age, composition of native herd, social experience, genetic origin, body condition and maternal dominance status. High-ranking individuals of both sexes were more aggressive, high-ranking males were older, and high-ranking females had a better body condition. Frequencies of aggressions were similar in both groups. The mares reacted significantly more by showing submission upon an aggression rather than by not responding or by escalating the aggression. For the geldings, this difference was not observed due to a lower tendency to submit. A linear dominance hierarchy was found in both groups. David’s scores provided additional information regarding cardinal rank distances and were used to calculate steepness of hierarchies. The female hierarchy was somewhat steeper compared to the male hierarchy, suggesting somewhat lower despotism among males. This was mainly a consequence of the lower unidirectionality in male submission. Male contests occurred predominantly between dyads at top and mid positions, suggesting a low degree of acceptance of the hierarchy.     

Male and female cooperatively breeding fish provide support for the "Challenge Hypothesis"

The idea that territorial aggression is regulated by androgensand that aggression itself can modulate androgen levels is wellestablished in males. In many species, females also displayaggressive behavior, yet little work has been conducted on theeffects of female aggression on hormone levels. In this study,we compared the effects of a simulated territory intrusion (amethod for testing the Challenge Hypothesis) on males and femalesof the fish, Neolamprologus pulcher. This cichlid fish fromLake Tanganyika is a particularly useful species to examinesex differences in the behavioral mediation of hormones as breedingpairs remain in a territory year round and both sexes defendthis territory against conspecific and heterospecific intruders.In our study, both sexes indeed aggressively defended theirterritory against a simulated territory intruder. In responseto intruders, both males and females displayed elevated levelsof circulating 11-ketotestosterone, but only females exhibitedincreases in testosterone. Neither aggressing male nor femalefish showed changes in estradiol levels compared to control(nonaggressing) fish. Residents were more aggressive than theintruders and won most of the interactions. However, residents(or winners) did not show higher hormone levels than intruders(or losers). We suggest that aggression commonly modulates androgenlevels in both male and female teleost fish.