Anna Karlsson

Female sand gobies gain direct benefits by choosing males with eggs in their nests

Abstract In some fish species with paternal care, females prefer to spawn with males whose nests already contain eggs. Several hypotheses have been put forward to explain this behaviour, such as reduced risk of predation or cannibalism (the dilution effect), increased parental investment, and mate copying. This experimental study focuses on female mate choice in the sand goby, Pomatoschistus minutus. Females were found to choose males with eggs in their nests. In addition, hatching success increased with clutch size, mainly because males with larger clutches showed less filial cannibalism. Increased egg survival in large clutches may thus be explained by a combination of the dilution effect and higher parental investment. In another experiment, females did not seem to copy the observed mate choice of other females. In conclusion, female preference for males with eggs in their nests is adaptive, and can be explained by direct benefits, as more surviving offspring are produced.

Mate choice in a hermaphrodite: you won't score with a spermatophore

Sexual selection has played a major role in shaping the wide variety of mating patterns found in species with separate sexes, but little is known about its effects on simultaneous hermaphrodites. However, many hermaphrodites possess complex reproductive systems and mating behaviour is often elaborate, suggesting that some form of mate assessment takes place. We found that the marine slug Aeolidiella glauca, a simultaneous hermaphrodite with reciprocal external sperm transfer via spermatophores, shows a unique mate choice behaviour by avoiding mating with conspecifics already carrying a spermatophore received during the previous mating. Current mating status did not seem to affect this behaviour, because both slugs that had mated 2–3 days before our mate choice trials and slugs that had been isolated for 4–6 weeks avoided spermatophore-carrying partners. There are two obvious reasons why slugs should avoid recently mated partners. First, they may reduce the risk of getting a partner depleted in self-sperm. Second, the risk of sperm competition may be decreased. Histological investigations of sperm reserves suggest that sperm depletion did not influence our mate choice experiments. Most slugs had sufficient sperm stored for spermatophore production. Therefore, the most likely explanation for A. glaucas peculiar mate choice is that, by avoiding a recently mated partner, a sperm donor may reduce its risk of being subjected to sperm competition.

Male wing shape differs between condition-dependent alternative reproductive tactics in territorial damselflies

Territorial contests between males without weaponry are based on costly displays and can result in condition-dependent alternative reproductive tactics that maximize male fitness. Physiological and morphological traits such as fat content, body size or the expression of secondary sexual traits have been shown to contribute to male territory-holding potential. When territorial contests are based on flight displays, wing morphology is expected to contribute to the territory-holding potential of a male through its effects on flight performance. We explored whether wing shape contributed to the territory-holding potential of males of three species of Calopteryx damselflies. Males of these species show two distinct, condition-dependent behavioural tactics: territorial and nonterritorial. Previous studies have shown that territorial males have higher fitness than nonterritorial males. We used mark–recapture to determine male tactics within the populations and compared wing shape, size and wing coloured spot size (a secondary sexual trait) between tactics. Territorial males of all three species had shorter and slightly broader hindwings than nonterritorial males. In two species, forewings of territorial males were longer and broader than forewings of nonterritorial males. Wing size and wing spot size did not differ between tactics. We suggest that the wing shape of territorial males might confer better flight manoeuvrability, which would be advantageous for territorial contests. Therefore, wing shape is likely to be an important trait contributing to territory-holding potential in condition-dependent alternative reproductive tactics based on flight displays.