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For traits showing correlated evolution, one trait may evolve more slowly than the other, producing evolutionary lag. The species-pairs evolutionary lag test (SPELT) uses an independent contrasts based approach to detect evolutionary lag on a phylogeny. We investigated the statistical performance of SPELT in relation to degree of lag, sample size (species pairs), and strength of association between traits. We simulated trait evolution under two models: one in which trait X changes during speciation and the lagging trait Y catches up as a function of time since speciation; and another in which trait X evolves in a random walk and the lagging trait Y is a function of X at a previous time period. Type I error rates under 'no lag' were close to the expected level of 5%, indicating that the method is not prone to false-positives. Simulation results suggest that reasonable statistical power (80%) is reached with around 140 species pairs, although the degree of lag and trait associations had additional influences on power. We applied the method to two datasets and discuss how estimation of a branch length scaling parameter (κ) can be used with SPELT to detect lag. [ABSTRACT FROM AUTHOR]

With their striking predilection for perching on African ungulates and eating their ticks, yellow-billed ( Buphagus africanus) and red-billed oxpeckers ( B. erythrorhynchus) represent one of the few potentially mutualistic relationships among vertebrates. The nature of the oxpecker-ungulate relationship remains uncertain, however, because oxpeckers are known to consume ungulate tissues, suggesting that the relationship between oxpeckers and ungulates may also be parasitic. To examine this issue further, we obtained data on oxpecker preferences for different ungulate species, the abundance of ticks on these ungulates, and ungulate hide thickness. In support of the mutualism hypothesis, we found that both species of oxpeckers prefer ungulate hosts that harbor a higher abundance of ticks. We found no evidence that hide thickness-a measure of the potential for parasitism by oxpeckers-predicts oxpecker preferences for different ungulate species. Oxpeckers also prefer larger-bodied ungulates, possibly because larger animals have more ticks, provide a more stable platform upon which to forage, or support more oxpeckers feeding simultaneously. However, the preference for ungulates with greater tick abundance was independent of host body mass. These results support the hypothesis that the relationship between oxpeckers and ungulates is primarily mutualistic. [ABSTRACT FROM AUTHOR]

Focuses on a study which the examined the correlates of baseline white blood cell (WBC) counts using the larger International Species Information System database. Data on WBC counts and correlations with phylogeny; Discussion on comparative data on primate socioecological variables; Absence of behavioral counterstrategies to sexually transmitted diseases; Transmission mode and host-parasite interactions.

The amount of time asleep varies greatly in mammals, from 3 h in the donkey to 20 h in the armadillo. Previous comparative studies have suggested several functional explanations for interspecific variation in both the total time spent asleep and in rapid-eye movement (REM) or “quiet” (non-REM) sleep. In support of specific functional benefits of sleep, these studies reported correlations between time in specific sleep states (NREM or REM) and brain size, metabolic rate, and developmental variables. Here we show that estimates of sleep duration are significantly influenced by the laboratory conditions under which data are collected and that, when analyses are limited to data collected under more standardized procedures, traditional functional explanations for interspecific variation in sleep durations are no longer supported. Specifically, we find that basal metabolic rate correlates negatively rather than positively with sleep quotas, and that neither adult nor neonatal brain mass correlates positively with REM or NREM sleep times. These results contradict hypotheses that invoke energy conservation, cognition, and development as drivers of sleep variation. Instead, the negative correlations of both sleep states with basal metabolic rate and diet are consistent with trade-offs between sleep and foraging time. In terms of predation risk, both REM and NREM sleep quotas are reduced when animals sleep in more exposed sites, whereas species that sleep socially sleep less. Together with the fact that REM and NREM sleep quotas correlate strongly with each other, these results suggest that variation in sleep primarily reflects ecological constraints acting on total sleep time, rather than the independent responses of each sleep state to specific selection pressures. We propose that, within this ecological framework, interspecific variation in sleep duration might be compensated by variation in the physiological intensity of sleep. [ABSTRACT FROM AUTHOR]