Mating system drives negative associations between morphological features in Schistosomatidae

Morphology and mating behaviour in the millipede Megaphyllum unilineatum (C.L. Koch, 1838) (Myriapoda, Diplopoda, Julida) under laboratory conditions

Although morphological variation may have an effect on behaviour, there are only a few studies on julid millipedes in which the influence of the variability of some morphological traits on mating success has been explored. Hence, objectives of this study were to investigate mating behaviour in laboratory conditions and identify traits that could possibly be the target of pre-copulatory selection in the julid species Megaphyllum unilineatum. Behavioural sequences were quantified in three types of tests: a mating arena test, a female choice test, and a male choice test. Although the number of contacts with the first chosen partner (from the mating arena test) was greater than with newly offered individuals in choice tests, values of the sexual selection coefficient did not statistically confirm this preference. In addition, analyses of linear measurements (trunk height and width, length of the whole body, antennae, walking legs, and gonopod flagella) in individuals of different mating status were also conducted, as well as geometric morphometric analyses of size and shape of the antennae, heads, walking legs, and gonopod promeres and opisthomeres in such individuals. Antennal length and shape, head shape, and the walking legs shape, differed significantly, depending on the mating status of females. In males of different mating status, statistical significance was established only in the promere centroid size. The differences in certain behavioural sequences in M. unilineatum are similar to those previously reported in M. bosniense, while such similarity is not detected with respect to morphological variation in the mentioned species.

Exploring patterns of interspecific variation in quantitative traits using sequential phylogenetic eigenvector regressions

A number of metrics have been developed for estimating phylogenetic signal in data and to evaluate correlated evolution, inferring broad-scale evolutionary and ecological processes. Here, we proposed an approach called phylogenetic signal-representation (PSR) curve, built upon phylogenetic eigenvector regression (PVR). In PVR, selected eigenvectors extracted from a phylogenetic distance matrix are used to model interspecific variation. In the PSR curve, sequential PVR models are fitted after successively increasing the number of eigenvectors and plotting their R(2) against the accumulated eigenvalues. We used simulations to show that a linear PSR curve is expected under Brownian motion and that its shape changes under alternative evolutionary models. The PSR area, expressing deviations from Brownian motion, is strongly correlated (r= 0.873; P < 0.01) with Blomberg's K-statistics, so nonlinear PSR curves reveal if traits are evolving at a slower or higher rate than expected by Brownian motion. The PSR area is also correlated with phylogenetic half-life under an Ornstein-Uhlenbeck process, suggesting how both methods describe the shape of the relationship between interspecific variation and time since divergence among species. The PSR curve provides an elegant exploratory method to understand deviations from Brownian motion, in terms of acceleration or deceleration of evolutionary rates occurring at large or small phylogenetic distances.