Life histories of the Insectivora: the role of phylogeny, metabolism and sex differences

Life-history data for 63 species from the mammalian order Insectivora have been collated from the literature. These data were analysed for covariation and for correlations with body mass, brain mass and mass-specific resting metabolic rate. An independent contrasts method has been used to remove the effect of phylogeny. Due to uncertainties surrounding their evolutionary r elationships, 22 different phylogenies of insectivores have been used as a basis for comparative analysis. The results show that several key correlati ons between life-history variables are only significant when certain phylog enies are used, highlighting the problems of such analyses when the phyloge ny used is inaccurate. After removing the effect of phylogeny, relatively f ew significant correlations remain. Insectivores that have a high body mass have relatively lower metabolic rates, longer lifespans and longer gestati on lengths. There is some support for a fast-slow continuum in insectivore life-history evolution: there are some significant positive correlations be tween measures of growth rates (e.g. gestation length and age at weaning) a nd lifespan, and some negative correlations between growth rates and measur es of reproductive output. It is suggested that the seasonality of life of many insectivores may have played an influential role in the evolution of t he group, in particular in delaying the onset of sexual maturity. There is little indication that brain size influences life-history evolution in this order, but metabolism may play an important role. The energetic requiremen ts of maintaining high metabolic rates in small mammals such as insectivore s may be constraining life histories to a greater extent than occurs in lar ger mammals. This effect may have obscured the relationship between metabol ic rate and life histories in wider inter-order analyses. Finally, there is considerable evidence that sex differences play a large role in shaping in sectivore evolution, and it is suggested that this factor must be considere d more often in future studies of mammalian life histories in general.