Most data on aggressive encounters in varanid lizards are qualitative and often anecdotal. The few quantitative reports have not explicitly tested the predictions generated by game theoretical models of animal combat despite their apparent relevance. The goal of this paper was to investigate whether the patterns evident in varanid contests conform to the predictions of the sequential assessment game with special emphasis on the organization, duration, and outcome of the encounters. Several characteristics of monitor combat are consistent with the sequential assessment game. For instance, contests are organized into distinct phases, displays are repeated within each phase, and asymmetries play a crucial role in determining contest duration and outcome. However, data pertaining to a number of the sequential assessment game's most critical postulations are absent from the current varanid literature (e.g. the consistency of display intensity within each phase). As more quantitative data emerge, the applicability of the sequential assessment game to varanid contests may be better assessed.
During agonistic interactions, decisions about contest persistence can be informed by assessment of one’s own energy or time expenditure (self-assessment), one’s own expenditure combined with opponent inflicted costs (cumulative assessment), or through information exchange with an opponent (mutual assessment). Females and males can be expected to exhibit different strategies for contest resolution due to contrasting energetic requirements and resource valuation. We examined the assessment strategies crayfish employ during same-sex and mixed-sex fights. Two individuals interacted for 15 min, and fight duration and times spent at various intensity levels were quantified. Results indicated that both sexes employ a self-assessment strategy during same-sex fights. Evidence for assessment during mixed-sex fights was notably weaker, suggesting the resolution of mixed-sex fights involves different behavioural elements and/or sources of information. In species where mixed-sex fights are common year-round, the lack of common rules can lead to greater energy expenditure for both sexes.
Oestrogen (e.g., 17β-estradiol, E2) stimulates vitellogenesis, female sexual behaviour, and induces sex pheromone production throughout vertebrates. Therefore, the quantification of its role in any one these may prove challenging; particularly in taxa such as snakes where mating coincides with vitellogenesis. Studies examining steroid hormones in snakes are further confounded by the typical sampling interval (monthly) which is likely insufficient to observe the brief hormone fluctuations associated with an oestrus period. Thus, the relationship between oestrus and endogenous sex steroids in snakes remains equivocal. We sampled plasma E2 of 12 radio-equipped free-ranging adult female northern watersnakes (Nerodia sipedon) twice weekly during the 2008–2009 mating periods. Reproductive females experienced a large E2 surge coincident with shedding, movement, and male accompaniment indicating that endogenous E2 is involved in oestrus, a phenomenon that has previously not been documented in snakes.
Phenotypic flexibility is essential for organisms to respond to changing environments. Guppies experience light environments that alter their visibility to conspecifics and predators. We used guppies from populations with low rates of predation by fish, but which may be subject to avian predators, to test the hypotheses that conspicuous behaviors and the androgens that mediate them are reduced under high light, and that cortisol levels are increased under high light because the perceived risk is stressful. We found reduced courtship, potentially driven by the reduced female response to courtship, under high light. Aggression and testosterone levels were higher in the absence of females. We found elevated androgen and decreased cortisol levels following social interactions, but no relationship between hormones and behavior, and no influence of light level on hormones. We forward explanations for these results and advocate understanding the flexible response to light environments in a range of guppy populations.
The Egyptian tortoise Testudo kleinmanni was recently split into two species on the basis of apparent differences in shell morphology and markings. Testudo kleinmanni was restricted to areas west of the Nile river and a new form, T. werneri, was described which occurred east of the Nile river (Perälä, 2001). However, when the morphometric analysis on which this decision was based (Perälä, 2001) was adjusted to allow for experiment-wise Type I error, by using P-value corrections, the proportion of the 46 characters that differed significantly between the two populations fell from 36.9% to only 13% in males and from 39.1% to just 8.7% in females. We then conducted a new morphometric analysis using our own data set that showed minor significant variation in morphometric and plastron markings between populations. An analysis of mitochondrial DNA based on 393 base pairs of the 12S rRNA gene, also showed near uniformity of western and eastern populations. Genetic divergence was only 0.2%, with the only consistent difference being a single G – A substitution at position 205. Based on the revised interpretation of Perälä (2001) results, our morphometric analysis on our own data set, and the molecular evidence, the variation observed between populations is normal within a species and therefore T. werneri is not a distinct independent evolutionary lineage and should not be considered a separate species from T. kleinmanni.