The impact of nutritional quality and gut bacteria on the fitness of Bactrocera minax (Diptera: Tephritidae)

To examine how nutritional quality and resident gut bacteria interplay in improving the fitness of an oligophagous fruit fly, Bactrocera minax , artificial sucrose diets and full diets (sucrose, tryptone and yeast extract) were fed to flies with and without antibiotic supplementation. Furthermore, Klebsiella oxytoca and Citrobacter freundii were supplemented to sucrose-only diets. Flies were maintained in the laboratory and the fitness parameters, male and female longevity, number of copulations and female fecundity, were recorded. Full diet without bacterial depletion significantly increased fecundity and copulation. In the absence of gut bacteria, flies fed with full diets had significantly decreased mean fecundity and copulation rate. Flies that were fed with sucrose diet had a very low copulation rate and produced no eggs. Diet type and the presence of bacteria did not have any effect on the average longevity of male and female flies. Bacterial supplementation in sucrose diets did not improve any of the measured parameters. The results demonstrate that gut bacteria interact with diet to influence mating and reproduction in B. minax . Symbiotic bacteria significantly and positively impact reproduction in B. minax ; however, their impact can only be fully realized when the flies are fed with a nutritionally complete diet.

Copulation rate declines with mating group size in dusky dolphins (Lagenorhynchus obscurus)

Males in polygamous species often engage in intrasexual competition for mates. If females actively evade mating attempts, it may benefit males to cooperate to restrict female movement, as has been found in some mammals. We tested if male dusky dolphins (Lagenorhynchus obscurus (Gray, 1828)) cooperate or compete during group mating chases. If they cooperate, then the per-male probability of copulating should increase with group size; if they compete, then the probability should decrease. We followed mating groups by boat during the breeding season (October 2013 – January 2014) off Kaikoura, New Zealand. The copulation rate per male decreased with increasing group size and with the number of noncopulating males in proximity to a copulating female. Male dusky dolphins have multiple mates and appear to use sperm and exploitative scramble competition. Males may remain in mating groups despite competition because there are alliances within the groups, they are unable to exclude rivals from joining a group, the time and energy costs of searching for unescorted females exceed the costs of reduced mating opportunities in a group, they receive other direct or indirect benefits that offset the costs of reduced mating opportunities, or they are in the group largely for social learning rather than procreation.

The Frequency and Timing of Courtship and Copulation in Blackbirds, Turdus Merula, Reflect Sperm Competition and Sexual Conflict

In a long-term field study we estimated the number of copulations per pair in blackbirds at 24.2 in a single reproductive cycle. Thus it seems unlikely that the only function of copulation behaviour is just to guarantee fertilization. We considered three other hypotheses which might explain frequent pair copulation: (1) as an effect of sperm competition, (2) cooperation between pair members aiming at increasing joint production of offspring; or, (3) sexual conflict resulting in female manipulation of allocation of time and energy of the male. We found no positive correlation between the copulation frequency and reproductive performance, a result that essentially falsifies the cooperation hypothesis. Only two extra-pair copulations were recorded. However, attempts at forced extra-pair copulation were very common and a high pair copulation rate might have evolved in response to sperm competition. Alternately, relatively high copulation rate in the pre-fertile stage of the reproductive cycle and female control over timing and frequency of copulation (via solicitation of copulation and/or rejection of courtship by the male) also supports the sexual conflict scenario. We suggest that our findings support the idea that the female prolongs the period of sexual activity to induce her partner to guard her (which reduces sexual coercion from other males) and to monopolise his parental effort (the male while mate guarding cannot pursue extra-pair activity or search for better mating options).