Prioritizing Sex Recognition Over Learned Species Recognition: Hierarchical Mate Recognition in an Invasive Fish

Mate recognition is the process of identifying and assessing the appropriate species, sex or population of another individual for their suitability as a potential mate. Recognition may be innate or learned. Learning, the acquisition of knowledge or skills through experience, involves a relatively long-term change in behavioral responses. In this study we examined learned and innate mate recognition in invasive male mosquitofish, Gambusia holbrooki, interacting with female conspecifics and male and female native toothcarp, Aphanius iberus. Male mosquitofish directed no mating attempts at male toothcarp whereas numerous attempts were made toward female toothcarp. Male mosquitofish therefore differentiated between males and females, but initially did not distinguish between con- and heterospecific females. Neither the presence of a male toothcarp, nor the presence of a refugia affected the number of mating attempts received by females. However, by the second day males appeared to learn to more accurately direct their mating attempts, with larger female mosquitofish receiving the most attention, though smaller toothcarp females were still harassed. We propose that male mosquitofish, with a coercive mating system, are selected for persistence despite rejection by potential mates. In this scenario, the pool of potential mates may include heterospecifics whose avoidance of mating attempts may be ignored by male mosquitofish. It may thus be adaptive for male mosquitofish to prioritize sex recognition over species recognition: if one sex is recognized as a “non-mate” this will cut 50% from the pool of potential mates whereas recognition of a single species will remove many fewer potential mates from the pool. This innate sex recognition together with rapid learning of species identity may be a factor in the invasive success of mosquitofish.

Similar Is Not the Same – Mate Recognition in a Parasitoid Wasp

Finding and recognizing a suitable mate is a key prerequisite to reproductive success. Insects often recognize prospective mates using chemical cues and signals. Among these, cuticular lipids commonly serve for mate recognition at close range. The lipid layer on the surface of insects is comprised predominantly of cuticular hydrocarbons (CHCs), though more polar compounds may also be present. While the composition of the cuticular profile is typically species specific, many species additionally show differentiation between the sexes by sex specific compounds and/or compound ratios. It is often assumed that a clear sexual dimorphism of cuticular lipid profiles is a prerequisite for a potential function as sex pheromones. Both, sex specific single compounds or the profiles as a whole have been shown to serve as sex pheromones in parasitoid wasps. Here, we studied parasitoid wasps of the species Tachinaephagus zealandicus (Encyrtidae, Hymenoptera). Chemical analyses revealed that this species presents a case where males and females produce the same set of CHCs in similar relative amounts. To test whether these wasps nonetheless can use the cuticular lipids for close range mate recognition, we tested the reaction of males toward freeze-killed conspecifics. Males showed copulation behavior exclusively toward dead females, but not toward dead males. Dead females from which the cuticular lipids had been removed did not elicit copulation behavior by tested males. Reapplication of female whole body extracts restored bioactivity, and males reacted with copulation attempts as often as toward the freeze-killed females. Bioassays with lipid fractions revealed that only the CHC fraction was bioactive on its own. Here, again, males reacted to female, but not to male CHCs. Our results indicate that these wasps are capable of using CHCs for close range sex recognition despite the similarity of male and female profiles.

Handicap theory is applied to females but not males in relation to mate choice in the stalk-eyed fly Sphyracephala detrahens

Handicap theory explains that exaggeratedly developed sexual traits become handicaps but serve as honest signals of quality. Because very weak signals are less likely to provide benefits than to simply incur costs, it is interesting to elucidate how sexual traits are generated and developed during evolution. Many stalk-eyed fly species belonging to tribe Diopsini exhibit marked sexual dimorphism in their eye spans, and males with larger eye spans have larger bodies and reproductive capacities, which are more advantageous in terms of contests between males and acceptance for mating by females. In this study, we investigated the role of eye span in a more primitive species, Sphyracephala detrahens, in tribe Sphyracephalini with less pronounced sexual dimorphism. Male-male, female-female, and male–female pairs showed similar contests influenced by eye span, which was correlated with nutrition and reproductive ability in both sexes. During mating, males did not distinguish between sexes and chose individuals with larger eye spans, whereas females did not choose males. However, males with larger eye spans copulated repeatedly. These results indicate that, in this species, eye span with a small sexual difference does not function in sex recognition but affects contest and reproductive outcomes, suggesting the primitive state of sexual dimorphism.

Sex recognition and agonistic strategies of male and female crayfish

Intraspecific communication is essential for agonistic and mating behaviours. Agonistic strategy of males must change according to the sex of opponents and that of females is also dependent on their physiological state as to whether they are brooding or not. We have analysed here the agonistic encounters between pairs of male and female crayfish in various combinations to reveal the interaction between agonistic and mating behaviours. After male crayfish became dominant, they aggressively chased subordinate males with attacks, while they did not attack female opponents. Furthermore, the agonistic behaviour of males changed depending on whether females were ovigerous or not. On the other hand, two females showed intense combats despite being ovigerous or not. Crayfish discriminated the sex of opponents via chemical signals in the urine. However, the dominant and subordinate social order of crayfish had no effect on selecting mating partners.

Molecular Sex Identification in the Hardy Rubber Tree (Eucommia ulmoides Oliver) via ddRAD Markers

Eucommia ulmoides, also known as the industrially and medicinally important hardy rubber tree, is the sole species of Eucommiaceae. Nevertheless, its dioecious property hinders sex recognition by traditional morphological observation at very early developmental stages, thus inhibiting breeding and economic cropping. In this study, double-digest restriction site-associated DNA sequencing (ddRAD-seq) was applied to screen sex-linked molecular markers for sex identification and investigation of the sex determination system in 20 male and female E. ulmoides individual plants, respectively. In consequence, five candidate male-specific loci but no female-specific loci were predicated among the 183,752 male and 147,122 female catalogue loci by bioinformatics analysis. Subsequent PCR (polymerase chain reaction) amplification and Sanger sequencing examinations were performed on another 24 individuals, 12 for each sex, from a separate population. One ideal sex-linked locus, MSL4, was identified among the five putative male-specific loci that were found using ddRAD data. MSL4 is 479 bp in length and highly conserved in all the male individuals, suggesting its feature of being stable and repeatable. Our results also indicated that the sex of E. ulmoides is likely determined genetically. In short, this study provides a consistent and reproducible ddRAD marker (MSL4) that is able to discriminate male from female seedlings in E. ulmoides, which will be valuable for rapid breeding practice and better commercial production of this economically important tree.

The success in the short-distance communication for mating does not depend on chemical signals in the crustacean decapod Procambarus clarkii (Girard, 1852)

Pheromone-driven sex recognition has been widely documented in crayfish and a great deal of evidence supports the involvement of pheromones in their mating behaviour. This study investigates whether sexual interaction and mating success in the red swamp crayfish Procambarus clarkii are dependent on short-distance chemical communication between sexes, mediated by urine-borne pheromones. We compared the mating behaviour of intact animals that could release urine to chemically communicate in a natural way with that of urine-blocked animal pairs, for which chemical communication was precluded. Our results show that urine-borne pheromones are not critical for the reproductive success of P. clarkii, at least over the short-range distance (<1 m) considered in this study, during which the animals were confined in a restricted tank, facing one each other, and thus able to promptly mate. Under these experimental conditions, a lack of urine release neither precluded the occurrence, nor affected the duration of the different phases of mating behaviour. We conclude that short-distance chemical communication in P. clarkii is not a prerequisite for mating, and suggest that it could be affected by alternative sensory modalities, likely vision and/or acoustic signalling.

Chimpanzee face recognition from videos in the wild using deep learning

Video recording is now ubiquitous in the study of animal behavior, but its analysis on a large scale is prohibited by the time and resources needed to manually process large volumes of data. We present a deep convolutional neural network (CNN) approach that provides a fully automated pipeline for face detection, tracking, and recognition of wild chimpanzees from long-term video records. In a 14-year dataset yielding 10 million face images from 23 individuals over 50 hours of footage, we obtained an overall accuracy of 92.5% for identity recognition and 96.2% for sex recognition. Using the identified faces, we generated co-occurrence matrices to trace changes in the social network structure of an aging population. The tools we developed enable easy processing and annotation of video datasets, including those from other species. Such automated analysis unveils the future potential of large-scale longitudinal video archives to address fundamental questions in behavior and conservation.