Animal Welfare: Beyond Human Happiness

For animals capable of affective feelings (enjoyment and suffering), we should also be concerned with their welfare. Welfare biology studies at least three basic questions: Which (species are capable of welfare)? Whether (their welfare is positive)? How (to increase their welfare? As affective feelings entail energy costs, species not capable of making flexible choices are not capable of affective feelings. The fact that members of most species either starve to death or are eaten before successful mating, their net welfare is likely negative. We could decrease animal suffering by banning pointless cruelty and making the living conditions of our farmed animals better (like increasing cage sizes of chicken farming). However, the widespread reduction of extensive animal suffering including wild animals will largely have to be left after our significant scientific/technological, economic, and moral advances. Excessively strict guidelines on animal experimentation that inhibit scientific/technological advances may thus be counter-productive in animal salvation in the long run.

Silk-borne chemicals of spider nuptial gifts elicit female gift acceptance

Chemical communication is important in a reproductive context for conveying information used for mate recognition and/or assessment during courtship and mating. Spider silk is a common vehicle for chemical communication between the sexes. However, despite being well described in females, male silk-borne chemicals remain largely unexplored. Males of the spider Pisaura mirabilis silk-wrap prey (i.e. nuptial gifts) that is offered to females during courtship and eaten by the female during mating. Interestingly, rejected males often add more silk to their gift which leads to successful mating, suggesting the presence of silk-borne chemicals that facilitate female gift acceptance. To test this hypothesis, we offered females standardized gifts covered with male silk that was either washed in solvents or unwashed, respectively, to remove or not any chemically active components. We scored female gift acceptance, and as expected in the case chemicals that mediate female mating behaviour are present in male silk, females were more likely to accept gifts covered with unwashed silk. Our findings suggest that silk-borne chemicals of nuptial gifts prime female responses, potentially signalling male quality or manipulating females into mating beyond their interests given the occurrence of male cheating behaviour via nutritionally worthless gifts in this system.

Sexual deprivation modulates social interaction and reproductive physiology

In highly polyandrous species, where females mate with multiple males within a single fertility period, there is typically a high level of sperm competition. To cope with this challenge, males apply various behavioral and physiological strategies to maximize their paternity rates. Previous studies in Drosophila melanogaster established a link between the composition of the social environment and the reproductive success of individual male flies. While most studies until now focused on the adaptive responses of male flies to the presence of rival males, little is known about whether the outcomes of sexual interactions with female partners affect male-male social interactions in a competitive environment such as the social group. Here we show that repeated failures to mate promote a coordinated physiological and behavioral responses that can serve to increase paternity chances over mating rivals. We exposed male flies to sexual deprivation or successful mating and analyzed the behavioral repertoires of individuals within groups and the structure of their emerging social networks. We discovered that failures to mate and successful mating generate distinct emergent group interactions and structures, where sexually deprived males form low density social networks and actively minimize their encounters with other group members, while increasing their aggressive behavior. In addition, sexually deprived male flies elevate the production of seminal fluid proteins (known to facilitate post-mating responses in females) and extend mating duration upon mating with receptive females, altogether leading to reduced re-mating rates. Our results demonstrate the existence of a flexible mating strategy that may provide a short-term fitness advantage over competing rivals and pave the path for using simple model organisms to dissect the neurobiology of social plasticity as coping strategy to living in a highly dynamic environment as the social domain.

Supplemental Sugar Is Required for Sex Pheromone Biosynthesis in Mythimna separata

Supplemental nutrients of adult moths maximize moth fitness and contribute to the pollination of many plants. Previous reports have revealed that sugar feeding promotes to sex pheromone biosynthesis by increasing the haemolymph trehalose concentration in mating moths. Here, Mythimna separata adults were employed as a model to investigate the effect of sugar feeding on sex pheromone biosynthesis. Results showed that in virgin females, sugar feeding markedly increased the concentrations of trehalose, pyruvic acid, and acyl-CoA in pheromone glands (PGs), which in turn led to an increase in sex pheromone titer, female ability to attract males and successfully mating frequency in sugar-fed females. Consistently, sugar-fed females laid more eggs than water-fed females. Furthermore, the refeeding of starved females also caused significantly increase in the concentrations of trehalose, pyruvic acid, and acyl-CoA in PGs, thus facilitating a significant increase in sex pheromone production. Most importantly, RNAi-mediated knockdown of trehalase (leading to PG starvation) resulted in an increase in trehalose content, and decrease in the concentrations of pyruvic acid, and acyl-CoA in PGs, which in turn led to a decrease of sex pheromone titer, female ability to attract males and successful mating efficacy. Altogether, results revealed a mechanism by which sugar feeding contributed to trehalose utilization in PGs, promoted to significantly increased sex pheromone precursor by increasing the concentrations of pyruvic acid and acyl-CoA, and facilitated to sex pheromone biosynthesis and successful mating.

The mating rate of Drosophila suzukii reduction due to reproductive interference from Drosophila melanogaster

Background Drosophila suzukii is widely distributed. Research has revealed that the presence of Drosophila melanogaster can reduce the emergence and egg laying of D. suzukii. However, the reasons for these phenomena have not yet been reported. To investigate this issue, we sought to answer three questions: Can the presence of D. melanogaster reduce the longevity of D. suzukii? Does D. melanogaster dominate in larval interspecific competition with D. suzukii? Does reproductive interference occur between these species; i.e., do individuals of one species (e.g., D. suzukii) engage in reproductive activities with individuals of the other (e.g., D. melanogaster) such that the fitness of one or both species is reduced? Results The results showed that the adult offspring number of Drosophila suzukii was significantly reduced when this species was reared with Drosophila melanogaster. The larval interspecific competition had no significant effects on Drosophila suzukii longevity or population size. Surprisingly, Drosophila melanogaster imposed reproductive interference on males of Drosophila suzukii, which led to a significant decline in the rate of successful mating of the latter species. Conclusions The presence of Drosophila melanogaster causes the population size of Drosophila suzukii to decrease through reproductive interference, and the rate of successful mating in Drosophila suzukii is significantly reduced in the presence of Drosophila melanogaster.

The Drosophila Suzukii Mating Rate Decrease for the Reproductive Interference of Drosophila Melanogaster

Background: Drosophila suzukii has been widely distributed all over the world since 2008, and it is a harmful pest causing great economic loss in many countries. Previous research has found that the presence of Drosophila melanogaster could reduce the emergence and egg laying of Drosophila suzukii. In order to figure out the potential mechanism of this phenomenon, we studied three potential factors including lifetime, larval interspecific competition, and reproductive interference. Results: The results show that the Drosophila suzukii offspring number was significantly decreased when reared with Drosophila melanogaster. The lifetime and larval interspecific competition have no significant effect on the Drosophila suzukii population. Surprisingly, Drosophila melanogaster can cause reproductive interference with male Drosophila suzukii, which leads to a significant decline in the successful mating rate of the latter fruit fly. Conclusions: The presence of Drosophila melanogaster causes the Drosophila suzukii population to decrease through the effect of reproductive interference, and the Drosophila suzukii successful mating rate is significantly decreased for the existence of Drosophila melanogaster.

Assessing the evidence of ‘infertile’ sea turtle eggs

There is increasing concern about feminization of sea turtle populations resulting from female-biased production of hatchlings due to climate change and selective loss of males from other anthropogenic drivers. Extreme female-biased breeding populations would reduce the likelihood of successful mating and potentially result in high rates of infertile eggs. Infertile eggs are those in which none of the events between sperm penetration of the ovum and syngamy have occurred. Distinguishing between fertile and infertile eggs is challenging, especially in field conditions, and researchers often have relied on physical evidence gathered from unhatched eggs at the end of the incubation period, which likely have experienced tissue decomposition. We argue that infertility in sea turtle eggs can be demonstrated only by the absence of holes caused by sperm penetration of the inner perivitelline membrane; sperm bound between the inner and outer perivitelline membranes; nuclei in the blastodisc; embryonic tissue or membranes in egg contents; and/or the characteristic white spot on the egg exterior. Unhatched eggs can be examined at the end of the incubation period, but we recommend that studies specifically investigating infertility examine at least 20 oviposited eggs each from clutches laid by at least 20 different turtles at the peak of the nesting season.

Successful mating and hybridisation in two closely related flatworm species despite significant differences in reproductive morphology and behaviour

Speciation is usually a gradual process, in which reproductive barriers between two species accumulate over time. Reproductive traits, like genital morphology and mating behaviour, are some of the fastest diverging characters and can serve as reproductive barriers. The free-living flatworm Macrostomum lignano, an established model for studying sex in hermaphrodites, and its congener M. janickei are closely related, but differ substantially in their male intromittent organ (stylet) morphology. Here, we examine whether these morphological differences are accompanied by differences in behavioural traits, and whether these could represent barriers to successful mating and hybridization between the two species. Our data shows that the two species differ in many aspects of their mating behaviour, with M. janickei having a five-fold longer copulation duration, copulating less frequently, and having a longer and more delayed suck behaviour (a postcopulatory behaviour likely involved in sexual conflict). Interestingly, and despite these significant morphological and behavioural differences, the two species mate readily with each other in heterospecific pairings, often showing behaviours of intermediate duration. Although both species have similar fecundity in conspecific pairings, the heterospecific pairings revealed clear postmating barriers, as only few heterospecific pairings produced F1 hybrids. These hybrids had a stylet morphology that was intermediate between that of the parental species, and they could successfully backcross to both parental species. Finally, in a mate choice experiment we tested if the worms preferentially mated with conspecifics over heterospecifics, since such a preference could represent a premating barrier. Interestingly, the experiment showed that the nearly two-fold higher mating rate of M. lignano caused it to mate more with conspecifics, leading to assortative mating, while M. janickei ended up mating more with heterospecifics. Thus, while the two species can hybridize, the mating rate differences could possibly lead to higher fitness costs for M. janickei compared to M. lignano.

Defects in mating behavior are the primary cause of sterility in C. elegans males at elevated temperature

Reproduction is a fundamental imperative of all forms of life. For all the advantages sexual reproduction confers, it has a deeply conserved flaw: it is temperature sensitive. As temperatures rise, fertility decreases. Across species male fertility is particularly sensitive to elevated temperature. Previously we have shown in the model nematode worm C. elegans, that all males are fertile at 20°C but almost all males have lost fertility at 27°C. Male fertility is dependent on the production functional sperm, successful mating and transfer of sperm, and successful fertilization post-mating. To determine how male fertility is impacted by elevated temperature we analyzed these aspects of male reproduction at 27°C in three wild-type strains of C. elegans: JU1171, LKC34, and N2. We found no effect of elevated temperature on the number of immature non-motile spermatids formed. There was a weak effect of elevated temperature on sperm activation that may negatively impact sperm function. In stark contrast, there was a strong effect of elevated temperature on male mating behavior and sperm transfer such that males very rarely successfully completed mating when exposed to 27°C. Therefore, we propose a model where elevated temperature reduces male fertility due to the negative impacts of temperature on the somatic tissues necessary for mating. Loss of successful mating at elevated temperature overrides any effects that temperature may have on the germline or sperm cells.