Many hypotheses were advanced and tested in numerous selleck inhibitor taxa regarding possible direct and indirect fitness benefits that females might derive from polyandry (e.g. Keller & Reeve, 1995; Yasui, 1998; Jennions & Petrie, 2000; Möller & Jennions, 2001). Of course, multiple mating was recognized to have potential downsides as well (such as the risk of contracting sexually transmitted diseases), but overall the bulk of the research effort went into understanding why females (in addition to males) often take multiple mates. Recent

surveys of the literature on genetic parentage in ‘pregnant’ vertebrate and invertebrate animals (Avise & Liu, 2010, 2011; Avise, Tatarenkov & Liu, 2011) have confirmed that the majority of broods do indeed consist of multiple full-sib cohorts, meaning that a gestating parent typically had several successful mates. Much more surprising, however, were two additional genetic observations: (1) the overall numbers and frequency distributions click here of mates per brood proved to be remarkably similar across invertebrate and vertebrate taxa; and (2) numbers of mates per pregnancy (typically about 2–5) were much lower than they theoretically could have been given the resolving powers of the molecular markers employed and given the large brood sizes (often with dozens to thousands of embryos) in many of the species assayed. The authors

of these review articles concluded that the explanation probably has to do not only with the balance between the costs and benefits of multiple mating but also with the finite logistical opportunities for successful mating events during each breeding season or episode. Depending on the species, constraints on mate acquisition might include ecological and natural-history factors such as low population densities, short mating seasons, poor vagilities, lengthy courtships, and perhaps even post-copulatory phenomena such as sperm competition and cryptic female choice of sperm (Birkhead & Pizzari, 2002; Eberhard, 2009), the net effect

being to truncate mate numbers even in animal species with huge broods and high frequencies of polygamy. Such mating-constraint hypotheses can be viewed as null models for reproductive behaviors Liothyronine Sodium in nature (Hubbell & Johnson, 1987; Gowaty & Hubbell, 2009), in which case logistical considerations offer a different perspective on mating systems that might help to counterbalance traditional interpretations based on polyandry’s purported selective advantages. For example, before invoking a selective explanation for genetic polygamy in any focal species, an important question might be whether the mean number of successful mates per brooder statistically exceeds or does not exceed the suspected rate of mate encounters given each species’ particular biology and ecology.