Potential for CFC in Black Widows (Genus Latrodectus): Mechanisms and Social Context

Abstract

Understanding the causes of variation in paternity is an important goal of research in sexual selection. While much progress has been made in understanding the dynamics of pre-copulatory mate choice and competition, post-copulatory processes that affect paternity are much less well understood. Distinguishing cryptic female choice (CFC, biases in paternity due to female post-copulatory preferences) from sperm competition (SC, competition among ejaculates for fertilization) and particularly from sexual antagonistic coevolution (SAC, intersexual conflict over mating frequency or fertilization) is at best challenging, and at worst, may be impossible. One way forward is to identify taxa in which comparative approaches, field studies, and detailed mechanistic study are all tractable, as these may allow the design of critical tests of distinguishing predictions of these intertwined hypotheses at different levels of analysis. Here, we focus on the widow spiders , the approximately 30 species in the genus Latrodectus , as a promising group for future work on CFC. Latrodectus spiders are distributed worldwide and show a fascinating range of mating systems set in variable ecological and social contexts. We outline how some of the aspects of Latrodectus natural history and biology may favor CFC rather than (or in addition to) pre-copulatory choice. Moreover, inter- and intraspecific variation in the benefits of CFC may provide the opportunity for comparative and intraspecific studies. We then identify likely mechanisms of CFC in this genus and end by providing suggestive evidence for CFC in a few of the species that have been studied in detail. Although there is no evidence for sperm selection in the Latrodectus to date, female behavior can lead to biases in paternity via changes in copulation frequency, duration, and remating as a function of male courtship effort . In addition, although first-male sperm precedence mediated by the deposit of sperm plugs is common in this genus, females may be able to manipulate the success of this internal plug and retain the ability to cede paternity to later mates. Since relatively few Latrodectus species have been studied in detail, this discussion is necessarily suggestive, rather than conclusive. Nevertheless, the available data suggest increased focus on this genus may prove productive for examining causes and consequences of CFC.