Pitelka Award Winners

The information an animal gathers from its environment, including that associated with signals, often varies continuously. Animals may respond to this continuous variation in a physical stimulus as lying in discrete categories rather than along a continuum, a phenomenon known as categorical perception. Categorical perception was first described in the context of speech and thought to be uniquely associated with human language.

A male’s reproductive success often depends on both his phenotypic quality and the quality of the resources he controls. An important and longstanding challenge for evolutionary biologists has been to disentangle these 2 often-correlated factors. Here, we present a large multiyear, multipopulation field study along with complementary laboratory experiments aimed at disentangling the effects of male quality and nest quality in driving male reproductive success in the plainfin midshipman fish, Porichthys notatus.

In socially monogamous species, male fertilization-related behaviors are expected to be tuned to the fertile cycle of their social female. How a male adjusts his fertilization-related behaviors to his social mate’s fertile period is relatively well understood. However, the influence of the social mate’s fertility stage on a male’s extrapair siring success remains poorly studied.

One way in which secondary sexual traits can influence differential reproductive success is by playing a key role in the outcome of direct physical contests for mates. Here we describe an undocumented trait in a species of hummingbird with a lek mating system, the Long-billed hermit (LBH, Phaethornis longirostris ). The trait under consideration is a dagger-like structure at the bill tip, which we hypothesize is a secondary sexual trait that functions as a sexually dimorphic weapon.

Behaviors are commonly correlated between individuals in so-called “behavioral syndromes.” Between-individual correlations of phenotypic traits can change the trajectories of evolutionary responses available to populations and even prevent evolutionary change if underpinned by genetic correlations. Whether behavioral syndromes also influence the course of evolution in this manner remains unknown.

Contest behavior, where individuals compete directly against one another for access to limited resources, is widespread across animal taxa. In many cases, contests are settled though the use of noninjurious behavior such as agonistic signals and even fights that involve weapons are often resolved through processes of assessment and strategic decision making.

Aposematic insects conspicuously advertise their unprofitability to potential predators. However, when these prey initially evolved, they were likely to have been rare and presumably at a greater risk of being detected and killed by naive predators. Both kin and individual selection theories have been used in attempts to explain this apparent paradox, with much of the empirical research supporting kin selection–based theories.

Carotenoid-based plumage ornaments are typically considered to be sexually selected traits, functioning as honest condition-dependent signals of phenotypic quality, but few studies have addressed the function of carotenoid color variation in male contest competition. Using two experiments, we investigated the status signaling function of the variable (ranging from yellow to red) carotenoid throat patch (collar) in the polygynous, sexually dimorphic red-collared widowbird (Euplectes ardens).

Phylogenetic patterns of change in spider silk coloration provide insight into the selective pressures directing evolution of silks. Trends toward evolution of silks with low reflectance of ultraviolet (UV) light suggest that reduced UV reflectance may be an adaptation to reduce visibility of webs to insect prey. However, a test of the visibility of primitive and derived spider silks is lacking.

Male Australian redback spiders (Latrodtctus hasselti Thorell: Theriidae) place their abdomens directly over their mate's mouthparts during copulation, increasing the likelihood of sexual cannibalism. Male sacrifice may be adaptive because cannibalized males increase their paternity relative to those that are not eaten. Despite male sacrifice behavior, however, up to 50% of laboratory matings may end without sexual cannibalism.

Extrapair paternity is common in many birds, and it is now generally accepted that female choice plays an important role. However, die benefits that females obtain from extrapair paternity are much less dear. To test the hypothesis that females obtain indirect fitness benefits, we studied paternity in a blue tit population over 4 years. Extrapair paternity occurred in 31-47% of all nests and accounted for 11-14% of all offspring.

I studied age-related breeding performance of the cooperatively breeding Seychelles warbler (Acrocephalus sechellensis) on Cousin Island, Seychelles, during 14 years. The annual number of young that fledged is significantly related to territory quality and number of helpers in the breeding group. Accounting for these factors and for the partner's breeding experience, annual production of fledglings by breeding birds increases from 2 to 5 years and decreases beyond 5 years of age.

We investigated kin discrimination among larvae of Arizona tiger salamanders (Ambystoma tigrinum nebulosum) which occur as “typical” morphs that feed mostly on invertebrate prey and occasionally on conspecifics, and as “cannibal” morphs that feed primarily on conspecifics. When housed with smaller larvae that differed in relatedness, both cannibals and typicals preferentially consumed less-related individuals.