A meta-analysis on alternative mating tactics: when the main and the alternative yield similar reproductive success

In many species, individuals of the same sex exhibit different mating behaviours, a phenomenon known as alternative mating tactics (AMTs). These AMTs may occur in species in which morphology prevents individuals from adopting different tactics (fixed expression of AMTs) as well as in species in which individuals can alternate between them (flexible expression of AMTs). Regardless of the way different mating tactics are expressed, a key point to understanding the selective forces driving AMT evolution relies on identifying differences in the reproductive success between tactics. Empirical studies often indicate that individuals adopting the main tactic (generally the more aggressive) have higher mating success than those adopting the secondary tactic. However, while this is expected for species showing flexible expression of AMTs, the same should not hold for species showing fixed expression of AMTs. In species with fixed expression of AMTs, individuals adopting each tactic have morphological specialisations in acquiring mates that may be responsible for eliminating differences in reproductive success between tactics. Despite such expectations, a comprehensive investigation across species regarding differences in the reproductive success of AMTs is lacking. Using a meta-analytical approach, we investigated if there is a difference in the reproductive success between tactics and whether this difference is related to how these tactics are expressed (fixed or flexible). We focused on males since information on reproductive success for females with AMTs is still scarce. We hypothesised that (i) males adopting the main tactic have higher reproductive success than males adopting the secondary tactic, and (ii) the difference in reproductive success between tactics will be higher in species with flexible rather than fixed expression of AMTs. When all species were pooled, we found that males adopting the main tactic had a similar reproductive success to males adopting the secondary mating tactic. However, this trend changed between species with fixed and flexible expression of AMTs. In species with flexible expression of AMTs, males exhibiting the main tactic have higher mating success than those adopting secondary tactics, while in species with fixed expression of AMTs, males adopting distinct tactics have similar reproductive success. Thus, the widespread assumption that males adopting the main tactic have higher reproductive success than males adopting the secondary tactic may be restricted to species in which individuals can alternate between tactics during their lifespan. However, we found that most data on the reproductive success of males adopting AMTs is restricted to short reproductive windows and may not reflect differences in lifetime reproductive success between tactics. Therefore, we highlight the importance of examining the selective pressures associated with fixed and flexible expression of AMTs on lifetime reproductive success to attain a deeper understanding of AMT evolution.

An experimental field test of female defense in territorial male collared lizards

A widely held principle in behavioral ecological research is that polygynous social systems evolve either by direct male defense of females or male defense of resources, although which of these mechanisms applies in particular species is rarely examined experimentally. We tested the relative importance of female versus resource defense in polygynous territorial male collared lizards (Crotaphytus collaris). Using a novel experimental design, we temporarily removed some of the resident females from male territories to create a female-free removal zone, whereas resident females were left intact within a non-removal zone. We then compared activity of males within each zone during three experimental phases; before we removed females, for two days when females were absent, and the day after return of females. If males defend females directly, we expected them to adjust the location of their patrol and display within removal and non-removal zones depending on the presence/absence of females, whereas we expected no such change if males defend resources. Male activity in the removal zone generally decreased when females were removed but then increased when females were replaced, whereas we observed the opposite pattern in the non-removal zone. The observed shifts in the location of patrol and display in response to the presence/absence of females, while resources remained constant, indicate that polygynous male collared lizards defend females directly. Our results suggest that male collared lizards take advantage of strong female philopatry to relatively small areas by focusing their patrol and display activities where potential mates reside.