Climate change, multiple paternity and offspring survival in lizards

Recent work suggests that rising spring temperatures over recent decades have eliminated many lizard populations, and threaten many more worldwide. However, because ambient temperatures constrain activity times in ectotherms, warming conditions (as expected under global climate change scenarios) can increase the duration of seasonal opportunities for courtship and mating. Thus, in species where polyandry results in enhanced off- spring viability, a warming climate may not necessarily im- pair long-term survival. Our nine-year study of a sand lizard (Lacerta agilis) population near the northern range limit in Sweden revealed consistently higher incidence of multiple pater- nity of clutches in warmer years, and higher viability of offspring from multiply-sired clutches (presumably reflecting the advan- tages of more intense sperm competition). Any trend to warmer spring temperatures likely will benefit offspring viability in this system, by increasing a female’s opportunities to mate with addi- tional males. Many critical ecological traits are highly sensitive to ambient thermal conditions, and hence potentially will be modified by cli- mate change. A growing literature documents such effects on traits such as seasonal phenology, growth rates, and sex-determining systems (Kearney, Porter and Shine 2009; Telemeco, Elphick and Shine 2010). Ectotherms (cold-blooded animals) may be es- pecially vulnerable in such respect, because they are critically dependent upon ambient thermal heterogeneity for behavioral regulation of body temperatures and thus, local climatic condi- tions constrain the timing and intensity of fitness-relevant ac- tivities (Kearney, Porter and Shine 2009). Sinervo et al. (2010) suggest that rising spring temperatures over recent decades have eliminated many lizard populations, and threaten many more worldwide. However, the impact of this thermal shift may be very different in a cold-climate area (such as Sweden) than in a hotter area (such as Mexico, the basis for most of their analyses). In sites where operative temperatures are already close to critical thermal maxima for local reptiles, higher temperatures could be devastating. For example, animals in such an area may have little time per day when conditions are cool enough to allow activities such as mate-searching and foraging (Kearney, Porter and Shine 2009; Sinervo et al. 2010). In contrast, reptiles in cooler areas may benefit from higher temperatures, because the conse- quent ability to maintain relatively high body temperatures over longer periods may enhance organismal fitness via extended ac- tivity times and enhanced performance (Kearney, Porter and Shine 2009). Here we test the hypothesis that warmer weather increases offspring survival via elevated sperm competition (and not just as an effect of higher temperature per se).