Effect of social condition on behavioral development during early adult phase in Drosophila prolongata

Enrichment effects on growth, health, and reproduction in a single clone of the asexual Amazon molly, Poecilia formosa

This study examines the impact of two types of environmental enrichment on the growth of the Amazon molly (Poecilia formosa), a clonal fish species. We investigated the effects of two welfare-related enrichment factors: physical enrichment (presence of a halfpipe PVC and gravel substrate, E) and social enrichment (presence of visible neighbor fish, N). Fish were divided into four treatment groups: (1) both physical and social enrichment (EN), (2) no physical enrichment but social enrichment (nEN), (3) physical enrichment without social enrichment (EnN,), and (4) no enrichment (nEnN). Results showed that individuals, which received both types of enrichment, exhibited faster growth rates and lower early life mortality compared to the other groups, indicating improved health and welfare. However, this initial advantage did not persist into adulthood, suggesting that the benefits of enrichment may be stage specific. These findings highlight the importance of environmental factors in promoting welfare in a particular species, especially during early developmental stages. This study may have implications for early life-stage fish research indicating that some environmental factors may play a role in enhancing growth, reproductive competence, and reduced mortality. Enrichment effects on growth, health, and reproduction in a single clone of the asexual Amazon molly, Poecilia formosa.

Reproductive advantage of the winners of male-male competition in Drosophila prolongata

In the resource-defence mating system, where males compete for limited resources to acquire females, male traits associated with fighting ability are selected, leading to the evolution of sexual dimorphism. However, the evolution of sexual dimorphism is also driven by other mechanisms, such as female selection. Therefore, to elucidate the evolutionary mechanisms of male traits, it is necessary to clarify their contribution to fitness through male-male competition. In this regard, it is surprising that numerous studies on sexually dimorphic species have assumed the resource-defence mating system without directly examining the relationship between resource-defending behaviour and mating success. In a sexually dimorphic fruit fly, Drosophila prolongata, the presence of the resource-defence mating system has been suggested, but technical difficulties had prevented spatial quantification of the resource-defending behaviour. In this study, by using an automated behaviour analysis tool previously developed, we located the occurrence of male-male competition and courtship to investigate their relationship in D. prolongata, considering the position of food resources. We found that the male-male competition led to the exclusive occupation of resources, increasing the courtship opportunities of the resource holders. These results illustrate the importance of resource-defending for reproductive success in D. prolongata.

Fight outcome influences male mating success in Drosophila prolongata

The outcomes of preceding fights can influence the probability of winning a subsequent fight, known as the winner/loser effect. However, we know relatively little about how the experience of a preceding fight influences subsequent mating success. Here, we investigated the influence of preceding fight outcomes on subsequent mating behavior in a fruit fly Drosophila prolongata. Subordinate males mated less in two-choice mating assays, showing that the fight outcome predicts male mating success in this species. This tendency remained in a no-choice mating assay where direct interaction between the dominant and subordinate males was eliminated, suggesting that the mating disadvantage of the subordinate males was dependent on the experience of the previous fight rather than the direct interference by the dominant male. When a no-choice mating assay was performed before the fight, the prospective subordinate males mated at the same rate as the dominant males, confirming that the intrinsic male qualities in fighting and mating performances were independent of each other in our experiments. These results indicated that the experience-dependent changes in the subordinate males led to the reduced mating success.

An Indirect Cost of Male-Male Aggression Arising from Female Response

Animal behavior is often polymorphic between individuals within a population. A cost/benefit balance of a particular behavioral pattern may be influenced by social interaction with other individuals with different behavioral patterns. Males of a fruitfly, Drosophila prolongata, show genetically defined polymorphism in aggressiveness and boldness against rival males. Males of the H strain are highly aggressive, and their fights tend to escalate into boxing, the highest level of aggressive interaction. H males are also bold against sneaker males and do not hesitate to perform leg vibration (LV), a courtship behavior that is vulnerable to interception of the female by surrounding rival males. In contrast, males of the L strain rarely engage in boxing and do not perform LV in the presence of rival males. We examined their mating success in small experimental populations. The mating success of L males was higher in a pure L population than in a mixed population with H males, whereas that of H males was higher in a mixed population than in a pure H population. Notably, this 'cost of aggression' in a pure H population seemed not directly derived from the male-to-male interaction but was imposed by the female's response of escaping from fighting males, compromising the benefit of the resource monopolization as territory.

Meta-analysis reveals that animal sexual signalling behaviour is honest and resource based

Animals often need to signal to attract mates and behavioural signalling may impose substantial energetic and fitness costs to signallers. Consequently, individuals often strategically adjust signalling effort to maximize the fitness payoffs of signalling. An important determinant of these payoffs is individual state, which can influence the resources available to signallers, their likelihood of mating and their motivation to mate. However, empirical studies often find contradictory patterns of state-based signalling behaviour. For example, individuals in poor condition may signal less than those in good condition to conserve resources (ability-based signalling) or signal more to maximize short-term reproductive success (needs-based signalling). To clarify this relationship, I systematically searched for published studies examining animal sexual signalling behaviour in relation to six aspects of individual state: age, mated status, attractiveness, body size, condition and parasite load. Across 228 studies and 147 species, individuals (who were predominantly male) invested more into behavioural signalling when in good condition. Overall, this suggests that animal sexual signalling behaviour is generally honest and ability-based. However, the magnitude of state-dependent plasticity was small and there was a large amount of between-study heterogeneity that remains unexplained.