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Insects copulate multiple times not only with different mates but also with the same mate, which is called repeated copulation. It occurs as a repeated alternation between copulation and mate‐guarding, leading to the prolonged physical attachment between males and females. Particularly, in species where males forcefully grasp females, attempt to mate without courtship and exhibit repeated copulations, male and female morphological traits are expected to be associated with mating characteristics. In this study, we describe for the first time the detailed mating behaviour and patterns of repeated copulations in the water scorpion Nepa hoffmanni (Nepidae, Hemiptera). Nepa hoffmanni repeated copulation and guarding approximately 10 times on average. Over repeated copulations, copulation duration decreased while guarding duration increased, potentially due to decreased male sperm reserves and increased female mating reluctance. Additionally, we found that average guarding duration was positively associated with male leg length and negatively associated with female leg length. This suggests that shorter male legs may enhance courtship efficiency or intensity, while shorter female legs may be less effective at resisting male mating attempts, leading to a quicker initiation of subsequent copulations with the same partner. This indicates that the evolution of repeated copulations may be linked to the evolution of morphological characteristics. Therefore, our study provides novel insights into the evolution of the mating behaviour of water scorpions. We describe for the first time the detailed mating behaviour and patterns of repeated copulations in the water scorpion Nepa hoffmanni (Nepidae, Hemiptera). Over repeated copulations, copulation duration decreased while guarding duration increased. Additionally, we found that average guarding duration was positively associated with male leg length and negatively associated with female leg length.

In animals where males engage in multiple matings, sperm depletion can substantially reduce the reproductive success of both sexes. However, little is known about how successive matings affect sperm depletion, fertilization rates and mating behaviour. Here, we investigated this phenomenon under laboratory conditions. Medaka (Oryzias latipes), an externally fertilizing fish, is an ideal model to test predictions of sperm depletion because there are established methods to observe its mating and count sperm. Medaka males mated with multiple females (19 per day, on average; range, 4–27), experiencing significant sperm depletion, with sperm release declining markedly after the first few matings, reaching only 0.5–6.3% by the last mating of the day. Fertilization rates decreased, particularly after approximately 10 consecutive matings, although there was some recovery in the next-day’s matings. The decline in courtship effort and mating duration probably resulted from the males becoming increasingly fatigued. Despite the reduced sperm availability, females did not adjust their clutch size as a counterstrategy. These results suggest substantial reproductive costs for males and the potential for sexual conflict owing to limited sperm availability. For species with frequent successive mating, these findings highlight the need to reconsider reproductive strategies and their impact on sexual selection.

This paper describes the first case of successful polyterritorial polygyny in the European Blackbird Turdus merula. It was detected in an intensively studied color-banded population of European Blackbirds in Szczecin (northwestern Poland). Received 13 November 2016. Accepted 18 June 2017.

The function of insect external genitalia has played a significant role in exploring insect mating mechanisms and male fertilization strategies. However, due to the privacy of genital coupling, insect copulatory mechanisms have only been investigated in a few insect groups. In this study, we observed the mating behavior using freeze-fixated pairs in copula to reveal the copulatory mechanism of the longhorn beetle Moechotypa diphysis (Pascoe, 1871). At the beginning stage of mating, the male M. diphysis usually takes 30 min to control the female and then extends its median lobe and endophallus. Approximately 80% of males (19/24) of M. diphysis exhibit multiple expansions (the membranous endophallus expands and enters into the female genital tract), ranging from two to five times. There are two types of expansions: short ones lasting for 1.4 to 49 s and long ones ranging from 1.03 to 7.23 min. During copulation, male tarsi continuously grasped the female elytra, thorax, and abdomen to help the male to initiate and maintain copulation. Male genital structures are closely connected to female genital structures: the apical phallomere and flagellum on the male endophallus contacting the bursa copulatrix duct and the spermathecal duct of the female, and the abundant microstructures on the surface of the everted male endophallus directly anchoring the female genital tract. Finally, we discuss the possible reasons for the evolution of their complex mating-related structures. Our research will help to explore the evolutionary mechanisms of insect genital structures.

Mating behaviour of the leucosiid crab Pyrhila pisum was studied in the laboratory and tidal flats in Japan. Most males actively approached females. Males started guarding females without any courtship behaviour (pre-copulatory guarding). Males began copulation within several minutes. The copulation continued for about 1–2 h, following which males began post-copulatory guarding. This guarding lasted from almost 0 to over 3 days, but its duration was generally much longer than that prior to copulation. Release of guarding was not linked to ovulation by females. Long-term rearing experiments revealed that both sexes of P. pisum could copulate multiple times with various mates. Developmental stages of the embryos recorded from copulating ovigerous females widely varied; their timing of copulation may not be fixed. In the tidal flat, wandering males frequently contacted with other individuals, but without distinguishing single males, single females and pairs of P. pisum , or Hemigrapsus takanoi . Male P. pisum cannot recognize female conspecifics, and they approach their mates relying only on vision, without using any attractive cues from females. In cases in which males encountered pairing crabs, they successfully stole the females when the guardians were smaller than the challengers, suggesting that effectiveness of guarding depends on male size. Among the mating pairs, males tended to be larger than females, and the tendency of size-assortative mating was weak or absent. Therefore, the mating behaviour of P. pisum is not elaborate, although their guarding behaviour may contribute to improve success to some degree.

Hybridization events have long interested biologists because of their implications for species concepts and taxonomy. Documenting hybridization events is important because hybridization rates are commonly used as support for accepted taxonomic divisions. In July 2017, we observed a nest where a male Cerulean Warbler (Setophaga cerulea) and a female Black-throated Blue Warbler (Setophaga caerulescens) were feeding nestlings. The Cerulean Warbler and Black-throated Blue Warbler communicated with each other using song (male) and calls (female), similar to a non-hybrid pair of either parent species, and the pair was not observed to engage in aggressive behaviors toward each other. Interestingly, the Black-throated Blue Warbler is not known to breed in Indiana, although it is a regular migrant in the spring and fall. We describe the behaviors of the hybrid pair at the nest, provide photographs and audio recordings for documentation, and hypothesize that this instance of hybrid pairing may have occurred due to mate scarcity. Received 1 November 2017. Accepted 8 August 2018.

Hybridization is relatively common in galliforms. In many cases, these hybrids are thought to arise through failures in species recognition, but there are no documented observations of this occurring in the wild. On 1 May 2013. I observed a male Ruffed Grouse (Bonasa umbellus) engage in a courtship display directed toward a female Spruce Grouse (Falcipennis canadensis). This is the first documented case of mistaken species recognition by a Ruffed Grouse and reveals 2 novel aspects of their behavior: the sound of wing flapping might be used to localize conspecifics, and males can be prone to directing courtship toward other species. Received 12 July 2017. Accepted 2 September 2018.

Background Sexual conflicts over the post-mating fate of received ejaculate can favour traits in one sex that are costly to the other. Reciprocally mating hermaphrodites face unique challenges as they mate simultaneously in both the male and female role, potentially leading to receipt of unwanted ejaculate. Reciprocal mating can then give rise to postcopulatory female resistance traits that allow manipulation of received ejaculate. A putative example is the suck behaviour, observed in the flatworm genus Macrostomum . It involves the sperm recipient placing its pharynx over its own female genital opening and appearing to suck, likely removing received ejaculate after mating. The genus also contains hypodermically inseminating species that presumably exhibit unilateral mating and have not been observed to suck. Results Here, we examine the evolution of the suck behaviour in the Macrostomum genus, aiming to document the mating behaviour in 64 species. First, we provide videographic evidence that ejaculate is indeed removed during the suck behaviour in a reciprocally mating species, Macrostomum hamatum . Next, we show positive evolutionary correlations between the presence, duration and frequency of reciprocal mating behaviour and the suck behaviour, providing clear evidence that the suck behaviour co-evolves with reciprocal mating behaviour. Finally, we show an association between reproductive behaviour and reproductive morphology, suggesting that the reproductive morphology can be used to infer a species’ mating behaviour. Conclusions Together, our study demonstrates sexually antagonistic coevolution leading to the evolution of a postcopulatory behavioural trait that functions as a female counter-adaptation allowing individuals to gain control over received ejaculate in a hermaphroditic sexual system.

Osmia cornuta Latr. is largely managed worldwide for the pollination of orchard crops, playing a key role in the maintenance of healthy ecosystems and ensuring economic and social benefits for human society. The management techniques of this pollinator include the possibility of delaying emergence from cocoons after diapause, allowing for the pollination of later-blooming fruit crops. In this study, the mating behaviour of bees emerging at the natural time (Right Emergence Insects) and of late-emerged bees (Aged Emergence Insects) was described in order to test if a delay in emergence could affect the mating sequence of O. cornuta. Markov analysis of the mating behaviour revealed the occurrence of antenna motion episodes that were repeated in a stereotyped manner at regular intervals during the mating sequence of both Right Emergence Insects and in Aged Emergence Insects. Pouncing, rhythmic and continuous emission of sound, motion of antennae, stretching of the abdomen, short and long copulations, scratching, inactivity, and self-grooming were identified as the stereotyped behavioural units of a behavioural sequence. The occurrence of short copulations, the frequency of which increased with the age of bees, could lead to a failure in the reproduction of the mason bee.

The exposure to sublethally high temperature reduces reproductive performance in diverse organisms. Although this effect has been particularly emphasized for males or male reproductive functioning, it remains largely unknown whether the effect of heat on fertility is sex-specific. Here we examined the impact of sublethally high temperature on male and female functions in a simultaneously hermaphroditic snail species, Lymnaea stagnalis . Examining hermaphrodites is useful to evaluate the sex-specific impacts of heat exposure, since they possess male and female functions within a single individual, sharing genetic and environmental factors. Moreover, previously developed sex allocation theory allows us to compare the differential performance of sex functions. In this study, we exposed snails to 20°C (control), 24°C and 28°C for 14 days and assessed their egg and sperm production, sperm transfer, mating behaviour and growth. Both types of gamete production were significantly reduced by higher temperature, leading to an overall reduction of reproductive investment. By quantifying sex allocation, we furthermore revealed that the heat-stressed snails reduced the relative investment in their male function. This study illustrates that examining simultaneous hermaphrodites can provide significant insights for the impact of heat, and the proximate mechanism, on reproduction in diverse organisms.