Male mate choice and patterns of paternity in the polyandrous, sexually cannibalistic orb-web spider, Nephila plumipes

Abstract

Studies that investigate patterns of paternity in polyandrous species typically employ double-mating trials, in which the paternity share of each male is established by either the sterile male technique or using genetic markers. However, polyandrous females may mate with more than two males and, in some species, triple-mating trials produce different patterns of paternity from double-mating trials. We investigated patterns of paternity share in triple-mating trials of the sexually cannibalistic orb-web spider Nephila plumipes. These experiments reveal little quantitative changes to paternity share when more than two males mate with the female; the third male apparently diluted the fertilisation success of the second male but not of the first male. Sexual cannibalism had little impact on the fertilisation success of the first male, but greatly increased the fertilisation success of the third male. When offered a choice, males did not prefer to mate with virgin over mated females, but males that chose virgin females were significantly heavier than those that chose mated females.Z O 0 2 0 7 9 M a t e c h o i c e a n d p a t e r n i t y i n o r b -w e b s p i d e r s M . A . E l g a r e t a l .

Male copulation frequency, sperm competition and genital damage in the golden orb-web spider (Nephila plumipes)

“…First, larger males may be more likely to survive copulations that involve pedipalp breakage than smaller males. However, earlier experiments reveal no sizerelated patterns of male survival of sexual cannibalism in N. plumipes, either before or during copulation Elgar 2001, 2002;Elgar et al 2003b). Alternatively, larger males may be more likely to mate with the female than smaller males, either because females fail to copulate with smaller males, or because larger males exclude their smaller rivals.…”

“…Males of these species are typically cannibalised by the female during their second copulation, and male Argiope and L. hasselti are apparently physiologically incapable of using a palp more than once (Forster 1992;Sasaki and Iwahashi 1995;Andrade 1996;Foellmer and Fairbairn 2003;Herberstein et al 2005;Snow and Andrade 2005). Sexual cannibalism is also common in N. plumipes Elgar 2001, 2002;Elgar et al 2003b) but, unlike red-backs and Argiope, it is apparently not inevitable after the male's second copulation. This is also the case for N. fenestrata, in which males defend their females from rivals after their second and final copulation (Fromhage and Schneider 2005a).…”

“…Males of N. plumipes almost invariably copulate with a female only if she is consuming a prey item (Elgar and Fahey 1996), a behaviour that reduces the risk of sexual cannibalism (Fromhage and Schneider 2005b). Copulation is relatively brief in this species Elgar et al 2003b), so females are likely to be consuming the prey item after the first copulation has ceased, thereby providing an incentive for males to quickly initiate a second copulation. Finally, several studies of this and other species of Nephila reveal high levels of disappearance among males moving between webs (Vollrath 1980;Kasumovic et al 2007; but see Fromhage et al 2007).…”

“…While interpreting these kinds of data is notoriously difficult, it is possible that matesearching males suffer higher levels of mortality. The uncertainty of locating a second female, the competitive disadvantage of copulating once rather than twice with the same female (Elgar et al 2003b), and the possibility of being cannibalised before inseminating the second female (Elgar and Fahey 1996;Elgar 2001, 2002;, provides a compelling argument that selection will favour males that inseminate both reproductive tracts of a single female, rather than attempt to inseminate a single tract each of two females.…”

“…The sex ratio on individual webs can be very heavily skewed, with individual females being host to numerous males who may engage in competitive contests (Elgar and Fahey 1996). There is an opportunity for sperm competition because females can mate with several males (Elgar et al 2003b).…”