Scutation asymmetries in red-footed tortoise Chelonoidis carbonaria Spix, 1824 (Testudines: Testudinidae)

The ability of an individual to withstand random perturbations during its development is considered a good indicator of environmental and genetic stress. A common means of assessing developmental stability is through analysis of fluctuating asymmetry (FA) in bilateral traits. Tortoises, with their large, solid plastron, allow for measurement of body geometry. Their bilateral shell scutes are ideal candidates for asymmetries researches. With this issue in mind we assessed, as a preliminary study, levels of plastron scute asymmetry in a sample of 46 red-footed tortoise Chelonoidis carbonaria from Arauca, N Colombia. We found significative fluctuating asymmetry (FA) but no directional asymmetry, the former not increasing with carapace size and thus indicating that tortoise shells do not become increasingly asymmetrical with age, or in other words, signaling that FA is not being influenced by pholidosis (variability of scale cover mosaic according to the development of the scutes). Asymmetry in plastron shape, although not necessarily apparent at first glance, varied, with gender with males exhibiting higher levels of FA than females. Although we can not identify the potential sources of variation responsible for the observed patterns of developmental instability, we consider this detected form of asymmetry due to unfavorable environmental conditions.

Reach- and mat-scale differences in Microcoleus autumnalis (cyanobacterium) accrual along velocity and nitrate gradients in three New Zealand rivers

Proliferations of the toxic, mat-forming cyanobacterium Microcoleus autumnalis are an increasingly recognized problem in cobble-bed rivers worldwide. This study explored how flow and nutrient concentrations influence mat expansion. Microcoleus autumnalis was inoculated into cobbles placed in runs, riffles, and pools in three rivers with different nutrient conditions, and mat size was monitored over 21 days. The following hypotheses were tested: (i) mat expansion will reflect cover increases at the reach scale; (ii) biomass and cover will be highest in high-velocity habitats; and (iii) under similar velocities, nutrient concentrations will be more important than other abiotic and biotic variables in determining expansion rates. Mat expansion accurately reflected the increase in reach-scale cover, and expansion was most rapid at intermediate water velocities (0.25–0.45 m·s–1). Mats persisted the longest in riffles. Accrual cycles were terminated earlier in runs than in riffles, as high expansion rates resulted in patches reaching maximum mat size rapidly. Although M. autumnalis accrual differed among rivers, this was attributed to differences in shear stress and grazing pressure rather than nutrient concentrations.

How could fully scaled carps appear in natural waters in Madagascar?

The capacity of organisms to rapidly evolve in response to environmental changes is a key feature of evolution, and studying mutation compensation is a way to evaluate whether alternative routes of evolution are possible or not. Common carps ( Cyprinus carpio ) carrying a homozygous loss-of-function mutation for the scale cover gene fgfr1a1 , causing the ‘mirror’ reduced scale cover, were introduced in Madagascar a century ago. Here we show that carps in Malagasy natural waters are now predominantly covered with scales, though they still all carry the homozygous mutation. We also reveal that the number of scales in mutated carps is under strong polygenic genetic control, with a heritability of 0.49. As a whole, our results suggest that carps submitted to natural selection could evolve a wild-type-like scale cover in less than 40 generations from standing polygenic genetic variation, confirming similar findings mainly retrieved from model organisms.