Sexual size dimorphism in the evolutionary context of facultative paedomorphosis: insights from European newts

Abstract

BackgroundSexual size dimorphism (SSD) is a key evolutionary feature that has been studied in many organisms. In a wide range of species, this pattern is more complex because of polymorphism within each sex. However, it is not known whether the magnitude and direction of SSD could be affected by alternative developmental trajectories within sexes. Our aim was to test whether an intrasexual polymorphism, facultative paedomorphosis (a process in which the development of somatic and gonadal tissues differs in alternative morphs), could affect SSD variation patterns in European newts.ResultsWe report here the first evidence that SSD varies depending on the paedomorphic or metamorphic ontogenetic pathway. In species with a consistent female-biased SSD, paedomorphosis decreased the SSD level, but did not affect its direction. In species with moderate female-biased SSD or variable SSD patterns, paedomorphosis changed the magnitude, or both the magnitude and the direction, of SSD.ConclusionOur study highlights the importance of developmental processes for shaping SSD patterns in populations in which contrasting life-history pathways evolved. European newts express different SSD patterns depending on their developmental pathway (i.e., metamorphosis versus paedomorphosis), as well as their species and population. These findings emphasize the importance of studying alternative morphotypes, which are found in a wide range of animal groups, to understand the evolution of SSD.

Heterochrony: the Evolution of Development

“…This can take the form of differences in average maximum size (1997) between males and females and/or differences in morphological features. This size and morphological variance arises from either variations in growth rates or differences in the relative times of onset of sexual maturity; in other words, it arises from heterochrony (see, for example, the work by Denoël et al (2009) on European newts). A relative modest example occurs in the Indian Ocean blue boxfish, Strophiurichthys robustus, where both male and female juveniles have a diamond-shaped body and a body pattern dominated by spots.…”

Life history trait differences between a lake and a stream-dwelling population of the Pyrenean brook newt (Calotriton asper)

“…In fact, there can be differences in the body size between paedomorphs and metamorphs depending on the population because environmental variables associated with the presence of paedomorphs can differ between species and populations (Denoël et al, 2009). For example, in some populations of newts {Lissotriton vulgaris, L. helvetieus and Iehthyosaura aipestris) paedomorphic forms can be smaller than the metamorphs or vice versa, as well as approximately identical (Denoël et al, 2009). In our case, the stream population was larger than the lacustrine population, which does not show different sizes between the gilled and metamorphic adults.…”

“…the potential for retention of juvenile traits in mature individuals) is an adaptive strategy found in most salamander families across heterogeneous environments caused by multiple ecological factors (Whiteman, 1994;Voss, 1995;Denoël, 2003). This strategy has been reported in several European newts of the genus Triturus (T cristatus, T. carnifex), Lissotriton (L. italicus, L. helveticus and L. vulgaris), Ichthyosaura alpestris and Omatotriton vittatus (Kalezic et al, 1996;Denoël and Joly, 2000;Denoël, 2003Denoël, , 2007Sindaco et al, 2006;Kaya et al, 2008;Denoël et al, 2009), demonstrating a wide occurrence among species with an apparent intraspecific geographic variation.…”

Proteomic evidence of a paedomorphic evolutionary process within a marine snail species: a strategy for adapting to extreme ecological conditions?

“…Paedomorphic patterns of evolution inferred from proteome analysis have been already reported for venoms of different snake species (see Calvete et al ., , ). Likewise, paedomorphic patterns have also been described in several salamander taxa by using morphological and anatomical comparisons and their evolutionary causes and consequences extensively discussed (Denoël et al ., , ; Doyle & Whiteman, ; Wiens & Hoverman, ). Although with some caution due to the differences in life and phylogenetic histories between salamanders and marine snails, we will try to extend the mentioned discussion in order to understand better this evolutionary pattern in the context of L. saxatilis populations.…”