The evolution of a complex trait: cuticular hydrocarbons in ants evolve independent from phylogenetic constraints

Cuticular hydrocarbons (CHCs) are ubiquitous and highly diverse in insects, serving as communication signal and waterproofing agent. Despite their vital function, the causes, mechanisms and constraints on CHC diversification are still poorly understood. Here, we investigated phylogenetic constraints on the evolution of CHC profiles, using a global data set of the species‐rich and chemically diverse ant genus Crematogaster. We decomposed CHC profiles into quantitative (relative abundances, chain length) and qualitative traits (presence/absence of CHC classes). A species‐level phylogeny was estimated using newly generated and previously published sequences from five nuclear markers. Moreover, we reconstructed a phylogeny for the chemically diverse Crematogaster levior species group using cytochrome oxidase I. Phylogenetic signal was measured for these traits on genus and clade level and within the chemically diverse C. levior group. For most quantitative CHC traits, phylogenetic signal was low and did not differ from random expectation. This was true on the level of genus, clade and species group, indicating that CHC traits are evolutionary labile. In contrast, the presence or absence of alkenes and alkadienes was highly conserved within the C. levior group. Hence, the presence or absence of biosynthetic pathways may be phylogenetically constrained, especially at lower taxonomic levels. Our study shows that CHC composition can evolve rapidly, allowing insects to quickly adapt their chemical profiles to external selection pressures, whereas the presence of biosynthetic pathways appears more constrained. However, our results stress the importance to consider the taxonomic level when investigating phylogenetic constraints.     

Disentangling phylogenetic from non‐phylogenetic functional structure of bird assemblages in a tropical dry forest

Understanding the factors driving assembling structure of ecological communities remains a fundamental problem in ecology, especially when focusing on ecological and evolutionary relatedness among species rather than on their taxonomic identity. It remains critical though to separate the patterns and drivers of phylogenetic and functional structures, because traits are phylogenetically constrained, but phylogeny alone does not fully reflect trait variability among species. Using birds from the Brazilian dry forest as a study case, we employed two different approaches to decompose functional structure into its components that are shared and non‐shared with the phylogenetic structure. We investigated the spatial pattern and environmental hypotheses for these phylogenetically constrained and unconstrained aspects of functional structure, including climate‐induced physiological constraints, historical climatic stability, resource availability and habitat partitioning. We found only partial congruence between the two methods of structure decomposition. Still, we found a differential effect of factors on specific components of functional structure of bird assemblages. While climate affects phylogenetically constrained traits through endurance, habitat partitioning (especially forest cover) affects the functional structure that is independent of phylogeny. With this strategy, we were able to decompose the patterns and drivers of the functional structure of birds along a semiarid gradient and showed that the decomposition of the functional structure into its phylogenetic and non‐phylogenetic counterparts can offer a more complete portrait of the assembling rules in ecological communities. We claim for a further development and use of this sort of strategy to investigate assembling rules in ecological communities.     

Intrasexual selection and phylogenetic constraints in the evolution of sexual canine dimorphism in strepsirhine primates

The goals of this study were to analyze the origin and function of sex differences in the size of canine teeth among Malagasy lemurs and other strepsirhine primates. These analyses allowed me to illuminate interactions between different mechanisms of sexual selection and to elucidate constraints on this sexually-selected trait. In contrast to central predictions of sexual selection theory, polygynous lemurs lack both sexual dimorphism in body size and male social dominance, but the degree of sexual dimorphism in the size of their canines is not known. A comparison of male and female canine size in 31 species of lemurs and lorises revealed significant male-biased canine dimorphism in only 6 of 13 polygynous lemur species. This result is in contrast to predictions of a hypothesis that would explain the lack of size dimorphism in lemurs as a result of high viability costs because canine teeth presumably have low maintenance costs and because they are used as weapons in male-male combat. Moreover, because females had significantly larger maxillary canines than males in only one lemur species, female dominance is not generally based on female physical superiority and selective forces favoring female dominance do not constrain sexual canine dimorphism in the sense of a pleiotropic effect. Contrary to predictions of sexual selection theory, species differences in canine dimorphism across strepsirhines were neither associated with differences in mating system, nor with the potential frequency of aggression. Variation in canine dimorphism was also unrelated to differences in body size, but there were significant differences among families, pointing to strong phylogenetic constraints. This study demonstrated that polygynous lemurs are at most subject to weak intrasexual selection on dental traits used in male combat and that traits thought to be under intense sexual selection are strongly influenced by phylogenetic factors.     

Within-species differences in primate social structure: evolution of plasticity and phylogenetic constraints

Primate socioecological studies have attempted to derive general frameworks using the average behavioural traits of species or genera to place them into categories. However, with the accumulation of primate studies, it is timely to place more emphasis on understanding within-species variation in social structure. In this review we have four objectives. First, we examine within-species variation in the potential determinants of social structure, including diet, demography, predation and infanticide, and document considerable variation. Second, we present case studies of within-species variation in social structure to illustrate the potential magnitude of this variation. For example, there are cases within a single interbreeding population where multi-male, uni-male, fission–fusion and monogamous groups are found. Third, by examining widespread primate lineages that occur in a variety of habitats, we note that there are differences in the magnitude of variation in social structures across different lineages and as a result we consider phylogenetic constraints on phenotypic variation in social structure. Finally, we reflect on the implications of extensive variation in social structure. We suggest that primate social structure will represent a combination of adaptation to present-day environment and phylogenetic inertia. To advance our understanding of the relative contribution of phylogeny versus ecology we propose two approaches. One approach is to compare groups in the same interbreeding population that inhabit different ecological conditions. Any differences that are found can be attributed to ecological differences, since phylogeny should not play a role within a single population. The second approach is to study distantly related species that have similar social structures to illustrate how similar ecological pressures might be operating to select for parallel social structures.     

Disentangling patch and landscape constraints of nested assemblages

The role of the matrix for the functionality of residual patches and therefore for species persistence has been recently recognised. However its influence on assemblage structure and composition is still unclear. We studied the effect of both patch and matrix attributes on community assemblage structure and composition in a fragmented landscape of central Italy. We used bird assemblages as a study model. Birds were sampled in 24 wood patches and distribution patterns were analysed considering both assemblage and guild-level responses. Patch composition and structure together with landscape patterns quantified with GIS were used as explanatory variables. The assemblages appeared to be strongly influenced by the landscape context, both in terms of composition and configuration. The functional connectivity of the patches, in terms of amount of neighbouring borders between woods and hedgerows, the shape of the woods in the matrix, together with the age of the patches, expressed as tree diameter, acted as the essential determinants, and even if the assemblages presented a significant nested structure, seven out of 40 species showed an idiosyncratic distribution. The study of the association between functional guilds and environmental parameters highlighted the influence of ecological constraints on the occurrence of unexpected presences and absences, suggesting the ability of some species to perceive and exploit matrix habitats. The matrix holds the capability to at least mitigate the effects of isolation and habitat loss, and the semi-natural elements of the mosaic may represent a biodiversity reservoir in an otherwise deprived landscape.     

DNA indels in coding regions reveal selective constraints on protein evolution in the human lineage

Background  

Insertions and deletions of DNA segments (indels) are together with substitutions the major mutational processes that generate genetic variation. Here we focus on recent DNA insertions and deletions in protein coding regions of the human genome to investigate selective constraints on indels in protein evolution.     

Floral scent evolution in the section Pseudophrys: pollinator‐mediated selection or phylogenetic constraints?

• Sexually deceptive orchid species from the Mediterranean genus Ophrys usually interact with one or a few pollinator species by means of specific floral scents. In this study, we investigated the respective role of pollinator‐mediated selection and phylogenetic constraints in the evolution of floral scents in the section Pseudophrys.
• We built a phylogenetic tree of 19 Pseudophrys species based on three nuclear loci; we gathered a dataset on their pollination interactions from the literature and from our own field data; and we extracted and analysed their floral scents using solid phase microextraction and gas chromatography‐mass spectrometry. We then quantified the phylogenetic signal carried by floral scents and investigated the link between plant–pollinator interactions and floral scent composition using phylogenetic comparative methods.
• We confirmed the monophyly of the section Pseudophrys and demonstrated the existence of three main clades within this section. We found that floral scent composition is affected by both phylogenetic relationships among Ophrys species and pollination interactions, with some compounds (especially fatty acid esters) carrying a significant phylogenetic signal and some (especially alkenes and alkadienes) generating dissimilarities between closely related Pseudophrys pollinated by different insects.
• Our results show that in the section Pseudophrys, floral scents are shaped both by pollinator‐mediated selection and by phylogenetic constraints, but that the relative importance of these two evolutionary forces differ among compound classes, probably reflecting distinct selective pressures imposed upon behaviourally active and non‐active compounds.

     

Intraspecific competition and the evolution of virulence in a parasitic trematode

Intrahost competition between parasite genotypes has been predicted to be an important force shaping parasite ecology and evolution and has been extensively cited as a mechanism for the evolution of increased parasite virulence. However, empirical evidence demonstrating the existence and nature of intraspecific competition is lacking for many parasites. Here, we compared within-host competitiveness between genetic strains of Schistosoma mansoni with high (HIGH-V) or low (LOW-V) virulence to their intermediate snail host, Biomphalaria glabrata. Groups of snails were exposed to either one or the other of two parasite strains, or a mixed infection of both strains, and the resulting progeny were identified using a molecular marker. In two separate experiments investigating simultaneous and sequential infections, we demonstrated that the lifetime reproductive success of parasite strain HIGH-V was reduced in the presence of a faster replicating parasite genotype, LOW-V, regardless of whether it was in a majority or minority in the initial inoculum of the simultaneous exposure or of its relative position in the sequential exposure experiment. Thus, we demonstrate competition between parasite genotypes and asymmetry in competitive success between parasite strains. Moreover, since the less virulent strain investigated here had a competitive advantage, we suggest that a high frequency of multiple infections could favor the evolution of less, rather than more, virulent parasites in this system.     

Reserve nutrients of the trematode Fasciola hepatica at various stages in its ontogeny

A comparative histochemical study for the presence of reserve nutrients (glycogen, fat) in tissues, organs of parthenitae (sporocysts, rediae) and larvae (miracidia, cercariae, adolescariae) of Fasciola hepatica from liver of sheep and cattle was carried out. The glycogen amount prevails at all developmental stages of Fasciola from sheep as compared to those from cattle. Fat was found in tissues and organs of parthenitae and larvae of this trematode in equal amount. Its reserves are obviously smaller than those of glycogen.     

Host-specific modulation of the selective constraints driving human immunodeficiency virus type 1 env gene evolution

To address the evolution of human immunodeficiency virus type 1 (HIV-1) within a single host, we analyzed the HIV-1 C2-V5 env regions of both cell-free genomic-RNA- and proviral-DNA-derived clones. Sequential samples were collected over a period of 3 years from six untreated subjects (three typical progressors [TPs] and three slow progressors [SPs], all with a comparable length of infection except one. The evolutionary analysis of the C2-V5 env sequences performed on 506 molecular clones (253 RNA- and 253 DNA-derived sequences) highlighted a series of differences between TPs and SPs. In particular, (i) clonal sequences from SPs (DNA and RNA) showed lower nucleotide similarity than those from TPs (P = 0. 0001), (ii) DNA clones from SPs showed higher intra- and intersample nucleotide divergence than those from TPs (P < 0.05), (iii) higher host-selective pressure was generally detectable in SPs (DNA and RNA sequences), and (iv) the increase in the genetic distance of DNA and RNA sequences over time was paralleled by an increase in both synonymous (Ks) and nonsynonymous (Ka) substitutions in TPs but only in nonsynonymous substitutions in SPs. Several individual peculiarities of the HIV-1 evolutionary dynamics emerged when the V3, V4, and V5 env regions of both TPs and SPs were evaluated separately. These peculiarities, probably reflecting host-specific features of selective constraints and their continuous modulation, are documented by the dynamics of Ka/Ks ratios of hypervariable env domains.     

ADH evolution and the phylogenetic footprint

The evolution of any given protein reflects the interplay between proximal selective forces involving the conservation of protein structure and function and more general populational factors that shape the action and efficiency of natural selection. In an attempt to address that interplay, we have analyzed patterns of amino acid replacement within a well-conserved molecule, alcohol dehydrogenase (ADH), in the Drosophilidae. A sliding window, moved along the protein sequence in order to quantify the extent of change at each amino acid position, reveals heterogeneous amounts of replacement across the molecule when all ADH sequences are analyzed simultaneously. Surprisingly, the replacement profile for ADH differs significantly in the melanogaster, mulleri, and Hawaiian subgroups, reflecting the imprint of the differing evolutionary histories of each of these assemblages on the evolution of this conservative molecule.Correspondence to: R.L. Dorit     

Genetic diversity and phylogenetic relations of salmon trematode Nanophyetus japonensis

Nanophyetiasis is the severe zoonotic disease caused by parasitic worms from the genus Nanophyetus. Humans and carnivorous animals become infected when they ingest raw fish containing metacercariae, especially Pacific salmonids. Nanophyetiasis is detected in limited geographical areas which include the coastal regions of the North Pacific: the United States of America, Russian Federation and Japan. Despite the epidemiological significance, Nanophyetus species have not been well studied genetically. In this research, we for the first time explored genetic diversity of Nanophyetus japonensis from Japan in comparison with those of related species, N. salmincola from North America and N. schikhobalowi from the Russian Far East, based on sequence variation in the nuclear ribosomal gene family (18S, ITS1–5.8S–ITS2 and 28S) and mitochondrial nad1 gene, encoding subunit I of the respiratory chain NADH dehydrogenase. The results confirmed the independent species status for the compared flukes, demonstrated a greater genetic similarity of Asian species between themselves than each of them with the North American one, suggesting that N. japonensis and N. schikhobalowi are close sister species, and also revealed discrepancy between the levels of morphological and genetic differentiation.     

Disentangling the selective factors that act on male colour in wild guppies

The colour pattern of male guppies ( Poecilia reticulata ) is thought to evolve as a compromise between sexual selection (favouring conspicuousness) and natural selection (favouring crypsis). Underpinning this classic explanation is the observation that guppies living with dangerous fish predators are less colourful than guppies living without these predators. However, high fish-predation sites are generally farther downstream than low fish-predation sites, and so may also differ in physical habitat features related to stream size, as well as in the abundance of predatory prawns ( Macrobrachium crenulatum ). The goal of our study was to disentangle the effects of fish predation on colour evolution from the potential effects of physical habitat features and predation by prawns. We collected 20 male guppies from each of 29 sites in two Trinidadian rivers. We then quantified the colour pattern of these fish; each spot was measured for size and assigned to a colour category. For each site, we determined the fish predation regime and quantified stream size, water colour, canopy openness, and prawn abundance. We then used regressions to assess the relative importance of these factors in explaining variation in guppy colour. Supporting previous work, the presence of predatory fishes was the most important explanatory variable for many components of colour pattern. Physical habitat features explained some of the remaining variation, but in inconsistent ways between the two rivers. The abundance of predatory prawns also explained variation in male colour. Our results suggest that predatory fishes impose the strongest selection on the colour pattern of male guppies but that other factors are also important.