Runaway social games,genetic cycles driven by alternative male and female strategies,and the origin of morphs

Analysis of evolutionarily stable strategies (ESS) and decade-long field studies indicate that two color morphs of female side-blotched lizards exhibit density- and frequency-dependent strategies. Orange females are r-strategists: they lay large clutches of small progeny that are favored at low density. Conversely, yellow females are K-strategists: they lay small clutches of large progeny that are favored when carrying capacity is exceeded and the population crashes to low density. Interactions among three male morphs resembles a rock-paper-scissors (RPS) game. Fertilization success of males depends on frequency of neighboring morphs. Orange males usurp territory from blue neighbors and thereby mate with many females. However, orange males are vulnerable to cuckoldry by sneaky yellow males that mimic females. The yellow strategy is thwarted in turn by the mate-guarding strategy of blue. Sinervo and Lively (1996) developed a simple asexual model of the RPS game. Here, we model the dynamics of male and female morphs with one- and two-locus genetic models. Male and female games were considered in isolation and modeled as games that were genetically coupled by the same locus. Parameters for payoff matrices, which describe the force of frequency-dependent selection in ESS games, were estimated from free-ranging animals. Period of cycles in nature was 5 years for males and 2 years for females. Only the one locus model with three alleles (o, b, y) was capable of driving rapid cycles in male and female games. Furthermore, the o allele must be dominant to the y allele in females. Finally, the amplitude of male cycles was only reproduced in genetic models which allowed for irreversible plasticity of by genotypes, which is consistent with hormonally-induced changes that transform some males with yellow to dark blue. We also critique experimental designs that are necessary to detect density- and frequency-dependent selection in nature. Finally, runaway ESS games are discussed in the context of self-reinforcing genetic correlations that build and promote the formation of morphotypic variation.     

The timing of birds' breeding seasons: a review of experiments that manipulated timing of breeding

Reproductive success usually declines in the course of the season, which may be a direct effect of breeding time, an effect of quality (individuals with high phenotypic or environmental quality breeding early), or a combination of the two. Being able to distinguish between these possibilities is crucial when trying to understand individual variation in annual routines, for instance when to breed, moult and migrate. We review experiments with free-living birds performed to distinguish between the 'timing' and 'quality' hypothesis. 'Clean' manipulation of breeding time seems impossible, and we therefore discuss strong and weak points of different manipulation techniques. We find that the qualitative results were independent of manipulation technique (inducing replacement clutches versus cross-fostering early and late clutches). Given that the two techniques differ strongly in demands made on the birds, this suggests that potential experimental biases are limited. Overall, the evidence indicated that date and quality are both important, depending on fitness component and species, although evidence for the date hypothesis was found more frequently. We expected both effects to be prevalent, since only if date per se is important, does an incentive exist for high-quality birds to breed early. We discuss mechanisms mediating the seasonal decline in reproductive success, and distinguish between effects of absolute date and relative date, for instance timing relative to seasonal environmental fluctuations or conspecifics. The latter is important at least in some cases, suggesting that the optimal breeding time may be frequency dependent, but this has been little studied. A recurring pattern among cross-fostering studies was that delay experiments provided evidence for the quality hypothesis, while advance experiments provided evidence for the date hypothesis. This indicates that late pairs are constrained from producing a clutch earlier in the season, presumably by the fitness costs this would entail. This provides us with a paradox: evidence for the date hypothesis leads us to conclude that quality is important for the ability to breed early.     

Behavioral ecology of disturbed landscapes: the response of territorial animals to relocation

Intraspecific territorial interactions are common for a largevariety of wildlife species. This often results in high-qualityhabitat being occupied by dominant individuals, with subordinatesrelegated to lower quality habitat. The role that these territorialinteractions play in influencing the redistribution of animalsthat have been evicted from their native home ranges remainsunclear. My goals were to determine (1) how the density of conspecificsin the new habitats impacts resettlement patterns and (2) towhat extent prior dominance status is maintained when an animalis forced to relocate. I relocated white-footed mice (Peromyscusleucopus) from high-quality, oak-dominated hardwood and lowerquality, white pine forests to novel sites and released themalong the ecotone of these two habitat types. I relocated micefirst in the presence and then in the absence of a natural densityof resident mice. Habitat selection and resource acquisitionof relocated mice were assessed via mark-recapture livetrappingand passive integrated transponder tagging. Relocated mice selectedhigh-quality habitat significantly more often when residentmice were absent, illustrating the importance of territorialinteractions for determining resettlement patterns of relocatedindividuals. Data on resource acquisition also reflected thecompetitive influence of resident mice—relocated micewere significantly more successful accessing food resourcesin the treatment without residents. The habitat of origin didnot significantly impact habitat selection or resource acquisition,indicating that all relocated individuals were at a disadvantagecompared to residents.     

Red coloration of male northern cardinals correlates with mate quality and territory quality

I investigated how mate quality and territory quality influenceanextravagant ornament in a socially monogamous species thatdefendsmultipurpose territories. Northern cardinals (Cardinaliscardinalis)are a highly dichromatic, socially monogamous species,and males are abrilliant red. I conducted a 3-year field studyof northern cardinals andfound that redder males produced moreoffspring in a breeding season. Twoselective factors mediatedthis fitness gain. Redder males were paired withearlier breedingfemales, an established measure of mate quality in birds.Second,redder males obtained territories of higher quality, as measuredbyvegetation density. Interactions among these factors werealso important inexplaining variance in male reproductive success.Multivariate analysisindicated that earlier breeding increasedreproductive success independent ofterritory quality. In turn,territory quality contributed to male reproductivesuccess throughits effect on nest survival and possibly through its role inattractingan earlier breeding female.     

Sequential settlement and site dependence in a migratory raptor

Habitat selection models, such as the ideal free, ideal despotic,site-dependent, and conspecific cuing models, are of great importanceto behavioral ecologists given their capability to predict habitatdistributions and to link individual behavior to populationprocesses. However, there have been relatively few field testsof their predictions. We tested the 4 models by studying theprocess of sequential settlement on territory in 2 distant populationsof a migratory raptor, the black kite Milvus migrans. Resultswere mainly consistent with the site-dependent model: on arrival,kites settled on progressively lower quality territories, andearlier arriving individuals were older, larger, and in betterbody condition than later arriving ones, leading to a state-dependentarrival sequence also predicted by a previous theoretical modelof settlement pattern. Occupation of superior territories bysuperior phenotypes resulted in cascading advantages for earlierarriving individuals in terms of subsequent reproductive performance.At the population level, the populations expanded/retractedfrom lower quality sites during population increases/declines.The above scenario was consistent across the 2 populations,and a review of the literature uncovered a remarkably consistentpicture of state-dependent arrival, progressive monopolizationof best quality sites, and cascading effects on subsequent breedingperformance. We propose as a general paradigm of sequentialsettlement the following process: 1) arrival date is a reliablesurrogate of phenotype quality, 2) early-arriving individualshave preferential access to the best quality sites and partners,3) the above conditions cascade into a number of benefits ultimatelyrelated to higher fitness for earlier arriving individuals.     

Ontogeny of sexual dimorphism and phenotypic integration in heritable morphs

In this study we investigated the developmental basis of adult phenotypes in a non-model organism, a polymorphic damselfly (Ischnura elegans) with three female colour morphs. This polymorphic species presents an ideal opportunity to study intraspecific variation in growth trajectories, morphological variation in size and shape during the course of ontogeny, and to relate these juvenile differences to the phenotypic differences of the discrete adult phenotypes; the two sexes and the three female morphs. We raised larvae of different families in individual enclosures in the laboratory, and traced morphological changes during the course of ontogeny. We used principal components analysis to examine the effects of Sex, Maternal morph, and Own morph on body size and body shape. We also investigated the larval fitness consequences of variation in size and shape by relating these factors to emergence success. Females grew faster than males and were larger as adults, and there was sexual dimorphism in body shape in both larval and adult stages. There were also significant effects of both maternal morph and own morph on growth rate and body shape in the larval stage. There were significant differences in body shape, but not body size, between the adult female morphs, indicating phenotypic integration between colour, melanin patterning, and body shape. Individuals that emerged successfully grew faster and had different body shape in the larval stage, indicating internal (non-ecological) selection on larval morphology. Overall, morphological differences between individuals at the larval stage carried over to the adult stage. Thus, selection in the larval stage can potentially result in correlated responses in adult phenotypes and vice versa.