Phylogenetic distribution of regeneration and asexual reproduction in Annelida: regeneration is ancestral and fission evolves in regenerative clades

Regeneration, the ability to replace lost body structures, and agametic asexual reproduction, such as fission and budding, are post‐embryonic developmental capabilities widely distributed yet highly variable across animals. Regeneration capabilities vary dramatically both within and across phyla, but the evolution of regeneration ability has rarely been reconstructed in an explicitly phylogenetic context. Agametic reproduction appears strongly associated with high regenerative abilities, and there are also extensive developmental similarities between these two processes, suggesting that the two are evolutionarily related. However, the directionality leading to this relationship remains unclear: while it has been proposed that regeneration precedes asexual reproduction, the reverse hypothesis has also been put forward. Here, we use phylogenetically explicit methods to reconstruct broad patterns of regeneration evolution and formally test these hypotheses about the evolution of fission in the phylum Annelida (segmented worms). We compiled from the literature a large dataset of information on anterior regeneration, posterior regeneration, and fission abilities for 401 species and mapped this information onto a phylogenetic tree based on recent molecular studies. We used Markovian maximum likelihood and Bayesian MCMC methods to evaluate different models for the evolution of regeneration and fission and to estimate the likelihood of each of these traits being present at each node of the tree. Our results strongly support anterior and posterior regeneration ability being present at the basal node of the annelid tree and being lost 18 and 5 times, respectively, but never regained. By contrast, the ability to fission is reconstructed as being absent at the basal node and being gained at least 19 times, with several possible losses. Models assuming independent evolution of regeneration and fission yield significantly lower likelihoods. Our findings suggest that anterior and posterior regeneration are ancestral for Annelida and are consistent with the hypothesis that regenerative ability is required to evolve fission.     

Genetic signature of the northward expansion of the Egyptian mongoose Herpestes ichneumon (Herpestidae) in the Iberian Peninsula

In the last three decades, the range of the Egyptian mongoose (Herpestes ichneumon) has increased in the Iberian Peninsula. A panel of microsatellites was used to confront the patterns of genetic diversity of the species with the scenario of its recent northward expansion in its Iberian range. Evidence of substructure and significant genetic differentiation within the studied population were recorded, with a central‐northern subpopulation (CNorth) and a southern subpopulation (S). Northward range expansion was supported by the observed allelic frequencies, diversity parameters, and observed heterozygosity of the studied loci, with S showing a higher allelic diversity and a higher number of private alleles than CNorth. Patterns of isolation‐by‐distance and isolation‐by‐barrier as a result of the Tagus River were demonstrated, suggesting that the river acted as a semi‐permeable barrier, possibly leading to genetic differentiation of the studied population. The observed individuals from CNorth in southern locations and individuals from S in central/northern areas might comprise evidence for long‐range dispersals across the studied range. A bottleneck event after population expansion was supported by a significant heterozygosity deficiency in CNorth, which is in agreement with a scenario of founder events occurring in recently colonized areas after the crossing of the Tagus River.     

MTPA: a crustacean metallothionein that affects hepatopancreatic mitochondrial functions

Metallothioneins are cysteine-rich proteins, with a high capacity to bind metallic ions, and for which a precise biological role has not been established. Here we investigated the effects of MTPA, a metallothionein from the lobster Panulirus argus, on mitochondrial oxygen consumption and ROS production. An HPLC-RP-ESI-MS analysis of recombinant MTPA showed that despite its extra Cys, MTPA binds 6 Zn²⁺ per molecule akin to other crustacean metallothioneins with 18 Cys. The extra Cys is not involved in zinc binding, since its side-chain would be oriented to the outside of the molecule according to a preliminary model of the tridimensional structure of MTPA. MTPA-Zn²⁺₆ is imported into the hepatopancreatic mitochondria intermembrane space and inhibits mitochondrial oxygen consumption, increasing thereby ROS production. Nevertheless, the stimulation of ROS production by MT-bound Zn²⁺ is weaker compared to equivalent amounts of free Zn²⁺, suggesting that MTPA protects against oxidative stress. This constitutes the first report on metallothioneins effects on mitochondrial function in invertebrates and agrees with the results described for mammals, suggesting a connection between metallothioneins and energy metabolism.