The danger within: the role of genetic,behavioural and ecological factors in population persistence of colour polymorphic species

Polymorphic species have been the focus of important work in evolutionary biology. It has been suggested that colour polymorphic species have specific evolutionary and population dynamics that enable them to persist through environmental changes better than less variable species. We suggest that recent empirical and theoretical work indicates that polymorphic species may be more vulnerable to extinction than previously thought. This vulnerability arises because these species often have a number of correlated sexual, behavioural, life history and ecological traits, which can have a simple genetic underpinning. When exacerbated by environmental change, these alternate strategies can lead to conflict between morphs at the genomic and population levels, which can directly or indirectly affect population and evolutionary dynamics. In this perspective, we identify a number of ways in which the nature of the correlated traits, their underpinning genetic architecture, and the inevitable interactions between colour morphs can result in a reduction in population fitness. The principles illustrated here apply to all kinds of discrete polymorphism (e.g. behavioural syndromes), but we focus primarily on colour polymorphism because they are well studied. We urge further empirical investigation of the genetic architecture and interactions in polymorphic species to elucidate the impact on population fitness.     

The stability of the species structure of the marine ciliate community to variations in environmental factors: The roles of physiological,population, and cenotic mechanisms

In field experiments on the transplantation of fragments of natural communities of marine ciliates into an estuary, restoration of the initial or modified species structure was observed after a short period of adaptation of the organisms. Their responses to new conditions included both species-specific reactions and group reactions (the synergistic effect). In a group, species are able to sustain larger amplitudes of variations in environmental factors than if they were separate and they can even occupy extreme biotopes. Under the conditions of the experiment, as well as in nature, a multitude of structural variants of the psammophile community (multivariability of structure) were created from the united pool of species through the recombination of their abundances. In total, the formation and maintenance of communities of unicellular organisms is determined by a complex mechanism that includes physiological (tolerance), population (reproductive properties), cenotic (interspecific interactions), and stochastic (reaction to environmental fluctuations) processes; their relative roles depend on the level of organization of the community (succession stage) and on the range of variations in environmental factors.     

Variation in the population structure between a natural and a human‐modified forest for a pioneer tropical tree species not restricted to large gaps

The distribution of tree species in tropical forests is generally related to the occurrence of disturbances and shifts in the local environmental conditions such as light, temperature, and biotic factors. Thus, the distribution of pioneer tree species is expected to vary according to the gap characteristics and with human disturbances. We asked whether there was variation in the distribution of a pioneer species under different environmental conditions generated by natural disturbances, and between two forests with contrasting levels of human disturbance. To answer this question, we studied the distribution patterns and population persistence of the pioneer tree species Croton floribundus in the size and age gap range of a primary Brazilian forest. Additionally, we compared the plant density of two size‐classes between a primary and an early successional human‐disturbed forest. Croton floribundus was found to be widespread and equally distributed along the gap‐size gradient in the primary forest. Overall density did not vary with gap size or age (F‐ratio = 0.062, P = 0.941), and while juveniles were found to have a higher density in the early successional forest (P = 0.021), tree density was found to be similar between forests (P = 0.058). Our results indicate that the population structure of a pioneer tree species with long life span and a broad gap‐size niche preference varied between natural and human‐disturbed forests, but not with the level of natural disturbance. We believe this can be explained by the extreme environmental changes that occur after human disturbance. The ecological processes that affect the distribution of pioneer species in natural and human‐modified forests may be similar, but our results suggest they act differently under the contrasting environmental conditions generated by natural and human disturbances.     

Drought resistance in early and late secondary successional species from a tropical dry forest: the interplay between xylem resistance to embolism,sapwood water storage and leaf shedding

The mechanisms of drought resistance that allow plants to successfully establish at different stages of secondary succession in tropical dry forests are not well understood. We characterized mechanisms of drought resistance in early and late‐successional species and tested whether risk of drought differs across sites at different successional stages, and whether early and late‐successional species differ in resistance to experimentally imposed soil drought. The microenvironment in early successional sites was warmer and drier than in mature forest. Nevertheless, successional groups did not differ in resistance to soil drought. Late‐successional species resisted drought through two independent mechanisms: high resistance of xylem to embolism, or reliance on high stem water storage capacity. High sapwood water reserves delayed the effects of soil drying by transiently decoupling plant and soil water status. Resistance to soil drought resulted from the interplay between variations in xylem vulnerability to embolism, reliance on sapwood water reserves and leaf area reduction, leading to a tradeoff of avoidance against tolerance of soil drought, along which successional groups were not differentiated. Overall, our data suggest that ranking species' performance under soil drought based solely on xylem resistance to embolism may be misleading, especially for species with high sapwood water storage capacity.     

Relations of intraspecific variations in fecundity, clutch size, and oviposition frequency to the body size in three species of stoneflies, Sweltsa sp., Isoperla aizuana, and Stavsolus japonicus

Most stoneflies oviposit several times during their adult stage. In this study, the relations among oviposition frequency, the number of eggs per egg mass, and body size were examined in the chloroperlid stonefly Sweltsa sp. and two perlodid stoneflies, Isoperla aizuana and Stavsolus japonicus. It was found that larger individuals tended to oviposit more frequently than smaller ones, but the relation was significant only in Isoperla aizuana. In Sweltsa sp. and Isoperla aizuana, the number of eggs per egg mass was higher for the less-frequently ovipositing individuals than for those ovipositing more frequently, and the number of eggs per egg mass decreased with successive oviposition events. Stavsolus japonicus showed the same tendency but it was not statistically significant.     

Mutational analysis of active‐site residues in the Mycobacterium leprae RecA intein,a LAGLIDADG homing endonuclease: Asp122 and Asp193 are crucial to the double‐stranded DNA cleavage activity whereas Asp218 is not

Mycobacterium leprae recA harbors an in‐frame insertion sequence that encodes an intein homing endonuclease (PI‐MleI). Most inteins (intein endonucleases) possess two conserved LAGLIDADG (DOD) motifs at their active center. A common feature of LAGLIDADG‐type homing endonucleases is that they recognize and cleave the same or very similar DNA sequences. However, PI‐MleI is distinctive from other members of the family of LAGLIDADG‐type HEases for its modular structure with functionally separable domains for DNA‐binding and cleavage, each with distinct sequence preferences. Sequence alignment analyses of PI‐MleI revealed three putative LAGLIDADG motifs; however, there is conflicting bioinformatics data in regard to their identity and specific location within the intein polypeptide. To resolve this conflict and to determine the active‐site residues essential for DNA target site recognition and double‐stranded DNA cleavage, we performed site‐directed mutagenesis of presumptive catalytic residues in the LAGLIDADG motifs. Analysis of target DNA recognition and kinetic parameters of the wild‐type PI‐MleI and its variants disclosed that the two amino acid residues, Asp¹²² (in Block C) and Asp¹⁹³ (in functional Block E), are crucial to the double‐stranded DNA endonuclease activity, whereas Asp²¹⁸ (in pseudo‐Block E) is not. However, despite the reduced catalytic activity, the PI‐MleI variants, like the wild‐type PI‐MleI, generated a footprint of the same length around the insertion site. The D122T variant showed significantly reduced catalytic activity, and D122A and D193A mutations although failed to affect their DNA‐binding affinities, but abolished the double‐stranded DNA cleavage activity. On the other hand, D122C variant showed approximately twofold higher double‐stranded DNA cleavage activity, compared with the wild‐type PI‐MleI. These results provide compelling evidence that Asp¹²² and Asp¹⁹³ in DOD motif I and II, respectively, are bona fide active‐site residues essential for DNA cleavage activity. The implications of these results are discussed in this report.