No water, no mating: Connecting dots from behaviour to pathways

Insects hold considerable ecological and agricultural importance making it vital to understand the factors impacting their reproductive output. Environmental stressors are examples of such factors which have a substantial and significant influence on insect reproductive fitness. Insects are also ectothermic and small in size which makes them even more susceptible to environmental stresses. The present study assesses the consequence of desiccation on the mating latency and copulations duration in tropical Drosophila melanogaster. We tested flies for these reproductive behavioral parameters at varying body water levels and with whole metabolome analysis in order to gain a further understanding of the physiological response to desiccation. Our results showed that the duration of desiccation is positively correlated with mating latency and mating failure, while having no influence on the copulation duration. The metabolomic analysis revealed three biological pathways highly affected by desiccation: starch and sucrose metabolism, galactose metabolism, and phenylalanine, tyrosine and tryptophan biosynthesis. These results are consistent with carbohydrate metabolism providing an energy source in desiccated flies and also suggests that the phenylalanine biosynthesis pathway plays a role in the reproductive fitness of the flies. Desiccation is a common issue with smaller insects, like Drosophila and other tropical insects, and our findings indicate that this lack of ambient water can immediately and drastically affect the insect reproductive behaviour, which becomes more crucial because of unpredictable and dynamic weather conditions.

Reproductive plasticity in both sexes interacts to determine mating behaviour and fecundity

Organisms alter their phenotype in response to variation in their environment by expressing phenotypic plasticity. Both sexes exhibit such plasticity in response to contrasting environmental and social cues, and this can reflect the influence of sexual conflict. However, theory predicts that plasticity expressed by both sexes may either maximise the sex-specific fitness of both, or of one sex at the expense of the other. Hence empirical tests of the predictions are sorely needed. Here we conducted novel tests of the fitness effects of interacting reproductive plasticity in Drosophila melanogaster. First, prior to mating, males were kept alone, or with same sex rivals, and females were kept alone, in same sex, or mixed sex groups. Second, we conducted matings between individuals from all these social treatments under ‘choice’ and ‘no choice’ scenarios. The results showed that males and females can both plastically respond to these socio-sexual environments to influence the expression of mating duration, mating latency, and fecundity. These plastic responses interacted significantly to determine mating latency and fecundity. Effects on mating latency were also observed under both choice and no-choice conditions, but in opposing directions. Variation in the outcome of interacting plasticity pivoted around the outcomes observed with focal females that had been maintained in same-sex environments prior to mating. However, not all fitness-related traits examined responded in the same way. Mating duration was determined largely by the social environment of the male. Our results show that the expression of some, but not all fitness-related reproductive traits can be determined by the outcome of interacting behavioural plasticity expressed by both sexes. This highlights the need for new predictive theory informed by these empirically-derived parameters. Overall, we conclude that variation in the expression of shared traits due to interacting plasticity represents an important and novel facet of sexual interactions.Impact SummaryAnimals and plants are able to respond to variation in their environment by expressing phenotypic plasticity. In sexual organisms, both males and females can exhibit such plasticity but the cues they respond to and the fitness consequences of these actions may be different between the sexes, and even conflicting. For example, males may respond to the presence of competitors by altering their mating behaviour or ejaculate transfer to increase their own, but not necessarily their mate’s reproductive output. However, females may also express phenotypic plasticity in response to their social and sexual environment to maximise their own fitness. Theory suggests that plasticity expressed by both sexes may either maximise the sex-specific fitness of both, or of one sex at the expense of the other. So far, little experimental work has been conducted to explore such interacting plasticity. Here we conducted novel tests of the fitness effects of interacting plasticity in the fruit fly Drosophila melanogaster. In doing so, we provide novel experimental evidence for interacting behavioural plasticity. We show that males and females can plastically respond to their socio-sexual environment to influence the expression of mating duration, mating latency, and fecundity. These plastic responses, while induced to increase the fitness interests of each sex, interact in the case of mating latency and fecundity and may reflect the outcome of sexual conflict. Our findings suggest that studies of reproductive behaviour should carefully consider the socio-sexual environment of both males and females and highlight the need for new predictive theory informed by empirically-derived parameters. Overall, we show that interacting plasticity between sexes represents an important and novel facet of sexual interactions.

No support for intra-nor inter-locus sexual conflict over mating latency and copulation duration in a polyandrous fruit fly

The total strength of sexual selection on males depends on the relationship between various components of pre- and post-copulatory fitness. Misalignment between male and female interests creates inter-locus sexual conflict, where the fitness of one sex is increased at the expense of the other. Although rarely considered, mating behaviours can also be genetically correlated between males and females, creating intra-locus sexual conflict, where beneficial alleles in one sex are costly when expressed in the other sex. How inter- and intra-locus sexual conflicts operate on the expression of mating behaviours remains little understood. Here, we study male attractiveness, mating latency and copulation duration in two populations of the polyandrous Drosophila serrata. Univariate analyses show little genetic variance in mating latency, and that males, but not females, contribute to copulation duration genetic variance. Further, multivariate analyses revealed little covariance between the studied traits. However, analyses considering male and female contribution in a single framework supported genetic contributions from both sexes for mating behaviours and complex patterns of between sexes correlations. Finally, our study did not find any association between those mating behaviours and fitness component, specifically (i) no phenotypic covariance between male attractiveness and mating latency and, (ii) longer copulations did not result in the production of more offspring. With no detectable fitness benefits in any sexes for shorter mating latency or longer copulation duration, our results do not support the presence of inter-nor intra-locus sexual conflict for these mating traits.

Effect of irradiation on the mating capacity and competitiveness of Drosophila suzukii (Diptera: Drosophilidae) for the development of the sterile insect technique

The sterile insect technique is a new approach for the integrated management of Drosophila suzukii Matsumura (Diptera: Drosophilidae), an invasive pest in North America. We evaluated, under laboratory conditions, the mating capacities and success of male D. suzukii, irradiated at a dose of 120 Gy, with and without competition. We also explored the tendency of females to remate depending if their first mate was irradiated or not. We observed that irradiated males have the same mating capacity as control males, copulating with, respectively, 6.4 ± 1.9 females versus 6.9 ± 2.0 females in a 24-hour period. Irradiated males won the competition 37.5% of times, which is not significantly different from competiveness of control males. Female remating can be considered infrequent and not significantly influenced by male treatment: 7.4% of the females first mated with control males and 18.8% of the females first mated with irradiated males remated when given the opportunity two days and four days after the first mating. Latency before mating and mating duration were not significantly influenced by male treatment, but by presence of male competition. Overall, irradiated males thus seem to be as performant as control males, which is an important condition for a successful sterile insect technique programme.

Low but genetically variable male remating ability in a tropical Drosophila despite substantial fitness benefits

Mating success is the main source of fitness variation in males, meaning that males should capitalise on all opportunities for mating. Strong selection on male mating success should also reduce genetic variation in male mating traits relative to other traits. We quantified mating latency, mating duration and productivity in males of the tropical fruitfly, Drosophila birchii, from 30 isofemale lines collected from across two elevational gradients, when they were given opportunities to mate with up to four females consecutively. Male remating rates were low compared to other Drosophila (only 14 – 27% of males achieved a fourth mating), with mean mating durations approximately doubling across successive copulations. However, although successive remating produced progressively fewer offspring, it consistently increased overall male reproductive success, with males that mated four times more than doubling offspring number compared to males mating only once. We also found no reduction in the productivity of sons emerging from later matings, indicating a sustained cumulative fitness benefit to remating. Heritable variation was observed for most traits (H2 = 0.035 – 0.292) except mating latency, but there was no divergence in trait means with elevation. The observed restricted remating ability of male D. birchii, despite the clear benefits of remating, may be due to a low encounter rate with females in the field, leading to high investment per gamete (or ejaculate). However, it remains unclear why genetic variation in these traits is high, given we observe no variation in these traits across elevational gradients known to affect local population density.

EFFECT OF NICOTINE ON SEXUAL BEHAVIOUR OF MUTANT STRAIN (CURLED) OF DROSOPHILLA MELANOGASTER

In the present study, an attempt was made to study the effect of plant extract on Sexual behaviour of Mutant Strain (Curled) of Drosophila melanogaster. The LC50 has been estimated with 1% of the food media. The virgin females and males were isolated and fed with normal food media for three days. Then sub-lethal concentrations of 0.625 μl / 100 ml food, 1.2 μl /100 ml food, 2.5μl /100 / food of nicotine were mixed in food medium and allowed in flies to feed for two days. Then appropriate combination of untreated / treated males and females were introduced into the mating chamber. Courtship latency, mating latency and copulation duration were studied. After observation of the behaviour, mated flies were allowed to produce progeny. The sexual behaviour of bachelor male and virgin female obtained in the progeny was also studied. The pooled data were analyzed by student t-test and the result indicates p-value significant at 0.05 levels. The courtship latency was affected by in treatment but it is neither dose dependent nor sex dependent.