A project undertaken at the Department of Biological Sciences, Macquarie University, and supervised by Anne Wignall, Marie Herberstein & Darrell Kemp
A fundamental assumption of sexual selection theory is that males will pass on their sexual traits to their offspring. That is, sexy father should sire sexy sons. While web-building spiders are often used as model species in sexual selection research, few studies have sought to understand the genetic basis of sexual behaviours in spiders [see Stratton & Uetz 1986].
Figure 1. Waveform of a section of a male web-building spiders’ courtship signal to a female (Argiope keyserlingi)
Figure 2. Adult male Argiope keyserlingi
Figure 3. Adult female Argiope keyserlingi
Male web-building spiders have complex vibratory courtship (Figure 1). Courtship consists of three main phases in which the male first enters the female’s web and cohabits with her at the centre of the web (the ‘hub’). The male then cuts out a section of web and builds a horizontal silk line in the gap (the ‘mating thread’). Finally, the male moves onto the mating thread and courts the female, generating vibrations by bouncing on the mating thread until the female climbs onto the thread (a characteristic position indicating her acceptance of the male as a mate). Recent research has shown that females base their assessment of male quality on his performance during courtship [Schneider et al. 2009]. While we do not yet understand very much about the information content of male courtship signals, males that court at higher rates are preferred as mates over males that court at lower rates. As a result, we predict that male courtship performance is under positive selection and heritable, passed from father to son.
We will examine the heritability of male courtship traits in web-building spiders, focusing on the St Andrew’s Cross spider, Argiope keyserlingi (Figures 2 and 3), a member of the orb-web spider family (Araneidae). We will also test the influence of male courtship performance on female mating preferences. Specific predictions that we will test include:
- Male courtship traits in web-building spiders are heritable from father to sons
- Female spiders will prefer males that perform better during courtship (particularly males that perform well in courtship behaviours that show the highest heritability in males)
- That males with high quality courtship will pass on indirect benefits to offspring, as indicated by offspring survivability and development time.
We will use a multidisciplinary approach to address these questions, combining techniques from behavioural ecology, biophysics and quantitative genetics.