Sperm competition theory predicts males should guard their mates with greater intensity when there is a higher risk of losing fertilizations. This relationship was tested in a spider, Nephila clavipes, first by evaluating factors (female age, mating status and duration of copulation with first male) that could affect the potential for sperm competition (likelihood of polyandry and sperm release by mating males) and second by relating this potential to intensity of post copulatory guarding. Female mating status influenced the potential for sperm competition (Study 1), but age did not when rematings were staged within a week after the female's normal two-day mating sequence with the first male (Study 2). Duration of copulation with the first male was an important influence on the potential for sperm competition (Study 3). When second males were presented four days after the female's final molt, longer durations with the first male reduced the likelihood of polyandry but did not influence sperm transfer. When second males were presented to females immediately after initial mating (Study 4), longer first male copulatory periods resulted in a reduced likelihood of polyandry and, when remating occurred, second males copulated for shorter durations, releasing fewer sperm. Hardening of the female reproductive tract, which occurs independent of mating, affected sperm release to only a minor degree (Study 5). Staged encounters revealed that postcopulatory guarding did vary, as predicted, with potential for sperm competition. Guarding intensity varied according to female status (Study 1) and, as expected, age of older, nonvirgin females did not influence intensity of defense (Study 2). When guarding trials were staged immediately after the first male had mated, intensity of defense was greater the shorter the first male's copulatory duration (Study 4). This coincided with the likelihood of polyandry and numbers of sperm released and consequently the potential for sperm competition. The nature of copulation and mate guarding in this species is consistent with sperm competition theory and appears not to result in conflict between the sexes / acase@tulane.edu
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_25241 |
| Date | January 2006 |
| Contributors | Linn, Christopher D (Author), Christenson, Terry E (Thesis advisor) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Rights | Access requires a license to the Dissertations and Theses (ProQuest) database., Copyright is in accordance with U.S. Copyright law |
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