Variation in morphological and behavioral traits among isofemale strains of Drosophila prolongata (Diptera: Drosophilidae)

Drosophila prolongata, a member of the rhopaloa subgroup of the melanogaster species group, occurs in Southeast Asia. Drosophila prolongata is known to have unique and prominent sexual dimorphism, with extraordinarily thick and elongated forelegs only in males. Mating behavior of D. prolongata is also characteristic: males perform “leg vibration” in their courtship toward females, in which the elongated forelegs play an important role. Comparisons with closely related species suggest that these morphological and behavioral traits have evolved rapidly after the divergence of D. prolongata. In the present study, variation in morphological and behavioral traits was examined among D. prolongata strains derived from single females collected in their natural habitats. Significant variations were detected in the size of various body parts, aggressiveness of interactions between males, and mating behavior. However, no obvious relationship was observed between morphological and behavioral traits. These results suggested that genetic factors contribute to the variation in morphological and behavioral traits in D. prolongata. The strains characterized in this study are useful for studies on the genetic mechanisms underlying the evolution of characteristic traits in D. prolongata.     

The courtship song of African Drosophila melanogaster

For many years it was thought that Drosophila melanogaster was relatively panmictic, without differentiation in the Mate Recognition System. Recent studies have demonstrated that flies from Africa vary in pheromones and assortative mating. Strains from Zimbabwe show strong sexual isolation from others. We show that the interpulse interval (IPI) of courtship song, an important mating signal, is unusually short among African flies. Zimbabwean flies have the shortest IPI, but there is no correlation with assortative mating, suggesting little direct role in sexual isolation. Chromosome replacements show that the IPI difference is largely due to genes on chromosome III, with significant interactions involving other chromosomes. Several traits potentially influencing sexual isolation among the melanogaster group of Drosophila seem to be localized to this chromosome. A concentration of important genetic differences might mean that the interaction effects reflect secondary coadaptation of the genetic background to changes associated with chromosome III.     

Experimentally induced variation in neuroendocrine processes affects male reproductive behaviour,sperm characteristics and social interactions

While extensive research has focused on how social interactions evolve, the fitness consequences of the neuroendocrine mechanisms underlying these interactions have rarely been documented, especially in the wild. Here, we measure how the neuroendocrine mechanisms underlying male behaviour affect mating success and sperm competition in the ocellated wrasse (Symphodus ocellatus). In this species, males exhibit three alternative reproductive types. “Nesting males” provide parental care, defend territories and form cooperative associations with unrelated “satellites,” who cheat by sneaking fertilizations but help by reducing sperm competition from “sneakers” who do not cooperate or provide care. To measure the fitness consequences of the mechanisms underlying these social interactions, we used “phenotypic engineering” that involved administering an androgen receptor antagonist (flutamide) to wild, free‐living fish. Nesting males treated with flutamide shifted their aggression from sneakers to satellite males and experienced decreased submissiveness by sneaker males (which correlated with decreased nesting male mating success). The preoptic area (POA), a region controlling male reproductive behaviours, exhibited dramatic down‐regulation of androgen receptor (AR) and vasotocin 1a receptor (V1aR) mRNA following experimental manipulation of androgen signalling. We did not find a direct effect of the manipulation on male mating success, paternity or larval production. However, variation in neuroendocrine mechanisms generated by the experimental manipulation was significantly correlated with changes in behaviour and mating success: V1aR expression was negatively correlated with satellite‐directed aggression, and expression of its ligand arginine vasotocin (AVT) was positively correlated with courtship and mating success, thus revealing the potential for sexual selection on these mechanisms.     

Mating tactics and male-male courtship in the lek-breeding cichlid Oreochromis mossambicus

Data are presented on the breeding behaviour of Oreochromis mossambicus under captive conditions. Males tended to synchronize their occupation of territories and breeding activities. Different male mating tactics were observed, namely establishing a breeding territory, acting as a floater, or behaving as a sneaker. The majority of spawnings observed involved dominant males and were subjected to interference from other males. Males were found to court other males that frequently responded to these attempts by adopting a female-like behaviour. Results are discussed in terms of a probable time constraint in territoriality, which promotes male-male competition and a low level of sex discrimination by territorial fish.     

Rapid courtship evolution in grouse (Tetraonidae): contrasting patterns of acceleration between the Eurasian and North American polygynous clades

Sexual selection is thought to be a powerful diversifying force, based on large ornamental differences between sexually dimorphic species. This assumes that unornamented phenotypes represent evolution without sexual selection. If sexual selection is more powerful than other forms of selection, then two effects would be: rapid divergence of sexually selected traits and a correlation between these divergence rates and variance in mating success in the ornamented sex. I tested for these effects in grouse (Tetraonidae). For three species pairs, within and among polygynous clades, male courtship characters had significantly greater divergence than other characters. This was most pronounced for two species in Tympanuchus. In the Eurasian polygynous clade, relative courtship divergence gradually increased with nucleotide divergence, suggesting a less dramatic acceleration. Increase in relative courtship divergence was associated with mating systems having higher variance in male mating success. These results suggest that sexual selection has accelerated courtship evolution among grouse, although the microevolutionary details appear to vary among clades.     

Small male mating advantage and reversed size dimorphism in poeciliid fishes

Despite interspecific differences in the absolute efficiency rate of copulatory thrusting in Poecilia reticulata, Phalloceros caudimaculatus, Heterandria formosa, Girardinus falcatus and Gambusia holbrooki small males had a significant advantage. These differences are discussed in the light of the interspecific differences in morphology and sexual behaviour. The results of the present study offer an alternative explanation for the pronounced reversed size dimorphism observed in this family of fishes. The greater efficiency of small males in achieving matings when females are unreceptive might also explain why genetically small males are maintained in natural populations of many poeciliids, in spite of the large size advantage in both intrasexual competition and female choice.     

Changes in courtship behaviour following rejection: The influence of female phenotype in Drosophila melanogaster

Courtship can be costly and so selection should favour individual males that reduce courtship towards female types that have a low probability of resulting in copulation. One way males can do this is by associating previous courtship failure with the traits of particular rejecting females. We characterised changes in male Drosophila melanogaster courtship behaviour following a failed mating attempt with one of the four female phenotypes that varied in size, age or mating status. To do this, we assessed individual courtship behaviour for each male presented again with a female of the same phenotype that previously rejected him. Males reduced subsequent courtship most strongly for recently mated (sexually non‐receptive) females. More interestingly, males also significantly reduced courtship activity following a failed mating experience from old females but did not do so for control (large, young, virgin) or small females. As such, males significantly reduced courtship towards both female types possessing chemical cues associated with their phenotype (age and mating status), but not towards a female phenotype based on physical characteristics (body size). Our results suggest that males are able to modify their courtship behaviour following experience, but that they are better prepared to associate chemical traits that may be more reliable indicators of the likelihood of courtship failure.     

The importance of sperm competition risk and nest appearance for male behavior and female choice in the sand goby, Pomatoschistus minutus

To test if an increased sperm competition risk affects malebehavior and mating decisions of both sexes, we performed twoexperiments using the sand goby, Pomatoschistus minutus, a nest-buildingfish with exclusive paternal care. In our first experiment,a nest-holding male, with a confined female, was sequentiallyexposed to a vial with a sneaker male or an empty vial. Whilemale courtship, nest building, displacement fanning, and timeoutside the nest were unaffected, individual males showed ahigher mucus preparation effort inside the nest in the presenceof a sneaker male than when alone. We found such mucus to containsperm, thus clearly suggesting an importance in sperm competition.In our second experiment, a female was free to spawn with twodifferent males, one of which was exposed to a confined sneakermale. Male mating success was not affected by the presence ofa sneaker male. However, the volume of sand the male had puton his nest was positively associated with female spawning decision,while nest-opening width was not. In a partial correlation offive traits thought to attract females (nest-opening width,sand volume, male courtship display, displacement fanning, andmale size), males that fanned well were found to also buildlarge nests or display intensely, but not both. This indicatesthat rather than being jacks-of-all-trades, individual malesfocus on a subset of traits for attracting females.     

Role of cell death in the formation of sexual dimorphism in the Drosophila central nervous system

Currently, sex differences in behavior are believed to result from sexually dimorphic neural circuits in the central nervous system (CNS). Drosophila melanogaster is a common model organism for studying the relationship between brain structure, behavior, and genes. Recent studies of sex‐specific reproductive behaviors in D. melanogaster have addressed the contribution of sexual differences in the CNS to the control of sex‐specific behaviors and the development of sexual dimorphism. For example, sexually dimorphic regions of the CNS are involved in the initiation of male courtship behavior, the generation of the courtship song, and the induction of male‐specific muscles in D. melanogaster. In this review, I discuss recent findings about the contribution of cell death to the formation of sexually dimorphic neural circuitry and the regulation of sex‐specific cell death by two sex determination factors, Fruitless and Doublesex, in Drosophila.     

Evolution of sexually dimorphic pheromone profiles coincides with increased number of male‐specific chemosensory organs in Drosophila prolongata

Binary communication systems that involve sex‐specific signaling and sex‐specific signal perception play a key role in sexual selection and in the evolution of sexually dimorphic traits. The driving forces and genetic changes underlying such traits can be investigated in systems where sex‐specific signaling and perception have emerged recently and show evidence of potential coevolution. A promising model is found in Drosophila prolongata, which exhibits a species‐specific increase in the number of male chemosensory bristles. We show that this transition coincides with recent evolutionary changes in cuticular hydrocarbon (CHC) profiles. Long‐chain CHCs that are sexually monomorphic in the closest relatives of D. prolongata (D. rhopaloa, D. carrolli, D. kurseongensis, and D. fuyamai) are strongly male‐biased in this species. We also identify an intraspecific female‐limited polymorphism, where some females have male‐like CHC profiles. Both the origin of sexually dimorphic CHC profiles and the female‐limited polymorphism in D. prolongata involve changes in the relative amounts of three mono‐alkene homologs, 9‐tricosene, 9‐pentacosene, and 9‐heptacosene, all of which share a common biosynthetic origin and point to a potentially simple genetic change underlying these traits. Our results suggest that pheromone synthesis may have coevolved with chemosensory perception and open the way for reconstructing the origin of sexual dimorphism in this communication system.     

Competition from large males and the alternative mating tactics of small males of dawson’s burrowing bee (Amegilla dawsoni) (apidae, apinae, anthophorini)

Males of Dawson’s burrowing bees (Amegilla dawsoni) search for virgin females at three locations: (1) open clay patches where females are emerging from underground brood cells, (2) the vegetated peripheral zone adjacent to emergence areas (through which females pass after emerging), and (3) clusters of flowering plants, which are often some distance from emergence areas. Males of Dawson’s burrowing bees exhibit a size dimorphism with large major and small minors. Major males patrol only the open emergence sites, whereas minor males may be found in all three locations. Although most females are mounted and presumably mated immediately upon emergence, some are not, and these females make up a pool of potential mates for the small males patrolling the peripheral zone and flower patches. The density of males at emergence sites and the probability of male-male aggression change over the course of a day and over the entire flight season. When the level of competition is low, some minor males hunt for mates at emergence areas, where potential mates are relatively numerous. But when the presence of many large rivals makes it unlikely that a small male can avoid being displaced from emerging females, minors make the best of a bad job by shifting to areas where majors are absent.     

Sexually dimorphic effect of mating on the melanotic encapsulation response in the harem‐defending Wellington tree weta,Hemideina crassidens (Orthoptera: Tettigonioidea: Anostostomatidae)

Reproductive activities are generally costly to immune responsiveness because limited resources required by reproduction are diverted away from immunity (and vice versa). Reproduction, however, is not expected to affect the immune response in males and females similarly as mating is expected to negatively affect male immunity more so than female immunity. Here, I test the phenotypic plasticity hypothesis in the Wellington tree weta (Hemideina crassidens), a sexually dimorphic orthopteran insect that is endemic to New Zealand. My laboratory experiment showed that although males had higher rates of melanotic encapsulation than females, contrary to prediction, females were the only sex significantly affected by mating and the effect was positive. In addition to immunity differing between the sexes, immune function can differ intrasexually, particularly when males are polymorphic and different investment strategies are used to maximize fitness. Male H. crassidens exhibit alternative mating strategies that are represented by three different morphotypes. I therefore explored whether the morphs differed in their melanotic encapsulation response and whether mating affected the morphs differently. I found no difference among morphs or an effect of mating on male immune response.     

The courtship behaviour of Yponomeuta padellus

The sequence of behavioural steps from male attraction until copulation is described and analyzed for Yponomeuta padellus L. (Yponomeutidae, Lepidoptera). Males respond to a pheromone emitting female with wing fanning followed by upwind zigzagging flight. Males will land near the females and then walk while wing fanning. The antennae drum onto the substratum and the abdominal-hair pencils are displayed. When in contact with a female the male drums with his antennae onto wings, head and antennae. Mostly a clasping attempt follows. A male has a higher chance to be accepted when he firt encounters the rear of a female instead of the head. Females refuse males by walking away or wing fanning or a combination of both.

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Résumé Les séquences du comportement depuis l'attraction du mâle jusqu'à la copulation ont été décrites et analysées chez Y. padellus (L.). Les mâles réagissent à une femelle émenttant une phéromone par un hattement d'ailes suivi d'un vol en zigzag contre le vent. Les mâles atterriront près des femelles et marcheront avec leurs ailes en battement. Les antennes tambourinent le substrat et les pinceaux abdominaux sont déplyés. Lorsqu'il est au contact de la femelle, le mâle tambourine avec ses antennes les ailes, la tête et les antennes. Généralement suit une tentative d'étreinte. Les chances de succès sont les plus élevées quand les premiers contacts du mâle sont avec la partie postérieure de la femelle plutôt qu'avec la tête. Les femelles refusent les mâles en s'écartant ou en battant des ailes ou les deux à la fois.Il semble qu'en plus des stimuli cliniques, des stimuli mécaniques fournis par les écailles sont nécessaires pour que les mâles localisent la femelle et s'orientent pour une tentative d'étreinte.

     

Courtship behaviour in the sandfly Lutzomyia longipalpis, the New World vector of visceral leishmaniasis

Courtship behaviour in Lutzomyia longipalpis Lutz and Neiva (Diptera: Psychodidae) was examined to determine the sequence of behaviours that occur prior to copulation. Courtship consisted of a series of male and female touching and wing-flapping behaviours, with males performing a greater variety of wing-flapping behaviours than previously described. Occurrence of male approach-flapping, semi-circling and female stationary-flapping were all predictors of eventual copulation, and may coincide with the dispersal of pheromones or the production of auditory signals important to courtship. Touching occurred in the majority of observations, with contact most often made with the tips of the legs and antennae. This behaviour, not previously described in sandflies, was initiated by males and females, and may indicate the use of contact pheromones, a form of communication previously overlooked in L. longipalpis. Future studies are required to separate the auditory and chemical signals associated with wing-flapping, and to confirm whether L. longipalpis possesses cuticular hydrocarbons capable of inducing behavioural responses. The identification of signals that inhibit sexual behaviour during courtship may be particularly relevant to developing mating disruption techniques against L. longipalpis.     

Sex‐specific evolution of relative leg size in Drosophila prolongata results from changes in the intersegmental coordination of tissue growth

Evolution of relative organ size is the most prolific source of morphological diversity, yet the underlying molecular mechanisms that modify growth control are largely unknown. Models where organ proportions have undergone recent evolutionary changes hold the greatest promise for understanding this process. Uniquely among Drosophila species, Drosophila prolongata displays a dramatic, male‐specific increase in the size of its forelegs relative to other legs. By comparing leg development between males and females of D. prolongata and its closest relative Drosophila carrolli, we show that the exaggerated male forelegs are produced by a sex‐ and segment‐specific increase in mitosis during the final larval instar. Intersegmental compensatory control, where smaller leg primordia grow at a faster rate, is observed in both species and sexes. However, the equilibrium growth rates that determine the final relative proportion between the first and second legs have shifted in male D. prolongata compared both to conspecific females and to D. carrolli. We suggest that the observed developmental changes that produce new adult proportions reflect an interplay between conserved growth coordination mechanisms and evolving organ‐specific growth targets.     

Cognitive ability is heritable and predicts the success of an alternative mating tactic

The ability to attract mates, acquire resources for reproduction, and successfully outcompete rivals for fertilizations may make demands on cognitive traits—the mechanisms by which an animal acquires, processes, stores and acts upon information from its environment. Consequently, cognitive traits potentially undergo sexual selection in some mating systems. We investigated the role of cognitive traits on the reproductive performance of male rose bitterling (Rhodeus ocellatus), a freshwater fish with a complex mating system and alternative mating tactics. We quantified the learning accuracy of males and females in a spatial learning task and scored them for learning accuracy. Males were subsequently allowed to play the roles of a guarder and a sneaker in competitive mating trials, with reproductive success measured using paternity analysis. We detected a significant interaction between male mating role and learning accuracy on reproductive success, with the best-performing males in maze trials showing greater reproductive success in a sneaker role than as a guarder. Using a cross-classified breeding design, learning accuracy was demonstrated to be heritable, with significant additive maternal and paternal effects. Our results imply that male cognitive traits may undergo intra-sexual selection.     

How not to be seen: does eutrophication influence three‐spined stickleback Gasterosteus aculeatus sneaking behaviour?

Experiments done in aquaria under control and either turbid or densely vegetated conditions indicated that three‐spined stickleback Gasterosteus aculeatus sneaking behaviour is affected by decreased underwater visibility. Success of sneaking behaviour decreased significantly under increased turbidity but not increased vegetation density. The total number of sneaking attempts, including unsuccessful ones, was not affected by either form of decreasing visibility.     

Sexual harassment in live-bearing fishes (Poeciliidae): comparing courting and noncourting species

Sexual harassment by males has been reported from several live-bearingfishes (Poeciliidae) and has been shown to inflict costs onfemales. For example, poeciliid females have reduced feedingopportunities when accompanied by a male because females dedicateattention to avoiding male copulation attempts. Poeciliid speciesdiffer considerably in male mating behavior, such as the presenceor absence of courtship. Courting males display in front ofthe females, but males attempting to sneak-copulate approachfemales from behind, that is, in the blind portion of theirvisual field, and force copulations, which can be viewed asa male persistence trait. We predicted that poeciliid femalesneed to be more vigilant in the presence of noncourting males,and costs of harassment by noncourting males might be stronger.In a comparative approach we examined the costs of male sexualharassment for females as reduced feeding time in 9 speciesof live-bearing fishes, including courting (Poecilia latipinna,Poecilia reticulata, Xiphophorus cortezi, Xiphophorus variatus)and noncourting species (Poecilia mexicana [surface- and cave-dwellingform], Poecilia orri, Gambusia affinis, Gambusia geiseri, Heterandriaformosa). In all species examined except for the cave form ofP. mexicana, focal females spent significantly less time feedingin the presence of a male than when together with another female.The time females spent feeding was found to significantly declinewith increasing male mating activity (sum of all sexual behaviors),but there was no support for the idea that females would spendmore time feeding in the presence of courting males comparedwith noncourting ones.