Evolutionary patterns of Clavatoraceae (Charophyta) in the mesogean basins analysed according to environmental change during Malm and lower cretaceous

Evolutionary patterns of Clavatoraceae during the Malm and the Lower Cretaceous can be understood by considering how palaeoecological constraints of these charophytes were affected by palaeoenvironmental change. Speciation of Clavatoraceae reached maxima in the Tithonian and especially in the Lower Barremian, coinciding with an important areal extension and environmental diversification of freshwater swamps. Extinction reached a peak in the Upper Barremian, coinciding with the marine flooding of freshwater environments in Mesogea, and continued through the Aptian and Albian due to substitution of carbonatic freshwater swamps by terrigenous deltaic environments and probably by development of highly competitive aquatic flora of angiosperms. Anagenetic change within species attained maxima during the Berriasian and Lower Barremian, when freshwater environments became extensively developed. Absence of change (stasis) was marked during the Valanginian and Hauterivian, in a geological context of environmental stability and areal reduction of the freshwater environments.     

A tale of time and depth: intralacustrine radiation in endemic Gammarus species flock from the ancient Lake Ohrid

Tentatively dated, the Plio‐/Pleistocene origin of the ancient Lake Ohrid on the Balkan Peninsula makes it the oldest ancient lake in Europe. Given the surface area of the lake and the adjusted endemicity rate, it may be also defined as the most diverse of all the ancient lakes in the world. From all the animal groups endemic to this lake, gammarids are amongst the most scarcely known in terms of their diversity and phylogenetic relationships. Partial DNA sequences of two mitochondrial genes, cytochrome oxidase subunit I (cox1) and 16S ribosomal RNA (16S rRNA) of eight known endemic Gammarus species from the Lake Ohrid valley were analysed. Phylogenetic analyses showed that endemic Gammarus species comprise an ancient species flock, with Gammarus sketi from the feeder springs being their sister taxon outside the lake. Amongst the species inhabiting the lake, Gammarus solidus and Gammarus salemaai are morphologically and molecularly well defined. By contrast, Gammarus ochridensis, Gammarus parechiniformis, Gammarus lychnidensis, and Gammarus stankokaramani revealed high discrepancy between morphological and genetic data. None of these morphospecies form a monophyletic clade and a significant degree of apparent gene flow occurs between them. This could be caused by incomplete lineage sorting and/or hybridization events. Two novel mtDNA lineages were found within the lake, possibly constituting two new species (Gammarus sp. 1 and Gammarus sp. 2). Molecular clock analysis showed that the split between G. sketi and the Gammarus species flock from the lake occurred approximately 5–7 Mya, whereas within the flock there were at least two intralacustrine radiations: one estimated at 2–3 Mya and the second at less than 1 Mya. The first one could be associated with the origin of the lake and the second with the lake water‐level fluctuations during Pleistocene. © 2013 The Linnean Society of London     

Geographical patterns of nucleotide diversity and population differentiation in three closely related European pine species in the Pinus mugo complex

Nucleotide polymorphism at 12 nuclear loci and two mitochondrial gene fragments was studied in three closely related pine species from the Pinus mugo complex in populations across the species distributional range in Europe. Despite large differences in the census sizes of the populations, high and similar levels of nucleotide diversity (θ_sil = ～0.013–0.017) were found at nuclear loci in the three pine species. More rapid decay of overall linkage disequilibrium (LD) and recombination to diversity ratio (ρ/θ) was observed across the species distributional range in P. mugo (ρ = 0.0369 ± 0.0028; ρ/θ = ～2.2) than in P. uncinata (ρ = 0.0054 ± 0.0011; ρ/θ = ～0.4) and P. uliginosa (ρ = 0.0051 ± 0.0010, ρ/θ = ～0.4). However, regional groups of P. mugo showed similar levels of LD and ρ/θ ratio to the other species. An excess of rare nucleotide variants was found in P. mugo at four loci, but, overall, the allelic frequency spectrum in the three species did not deviate significantly from neutrality (multilocus Tajima's D = ?0.681, D = ?0.118 and D = ?0.266, P > 0.05, respectively). Bayesian clustering methods showed no clear correspondence of clusters to species or geographical regions. Some differences between populations and species were found in a hierarchical analysis of molecular variance (AMOVA) and in the distribution of the mitochondrial DNA haplotypes, suggesting rather limited gene flow between the taxa and ongoing divergence. As all three pine taxa have similar genetic backgrounds, they form an excellent system for searching for loci involved in adaptive variation and speciation. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 225–238.     

Evolution of postzygotic reproductive isolation in galliform birds: analysis of first and second hybrid generations and backcrosses

The process of speciation is a crucial aspect of evolutionary biology. In this study, we analysed the patterns of evolution of postzygotic reproductive isolation in Galliformes using information on hybridization and genetic distance among species. Four main patterns arose: (1) hybrid inviability and sterility in F₁ hybrids increase as species diverge; (2) the presence of geographical overlap does not affect the evolution of postzygotic isolation; (3) the galliforms follow Haldane's rule; (4) hybrid inviability is higher in F₂ than in F₁ hybrids, but does not appear to be increased in the backcrosses. This study contributes to the growing evidence suggesting that the patterns of evolution of postzygotic isolation and the process of speciation are shared among avian groups (and animals in general). In particular, our results support the notion of F₂ hybrid inviability as being key for the maintenance of species genetic integrity when prezygotic isolation barriers are overcome in closely related species, in which postzygotic isolation in the F₁ hybrid might still not be fully developed. To the contrary, hybrids from backcrosses did not show serious inviability problems (at least not more than F₁ hybrids), demonstrating that they could generate gene flow among bird species. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 528–542.     

Intraspecific molecular phylogeny and phylogeography of the Meriones meridianus (Rodentia: Cricetidae) complex in northern China reflect the processes of desertification and the Tianshan Mountains uplift

The phylogeographical patterns and demographic history of mitochondrial DNA (cytochrome b, N = 327; D‐loop, N = 252) and nuclear DNA (IRBP gene, N = 235) haplotypes were studied for the Meriones meridianus complex in northern China, a desert‐dwelling gerbil species complex. The phylogenetic analyses, which were performed on the separate and combined (mitochondrial + nuclear) datasets, revealed two divergent clades (Clade A and Clade B) corresponding to distinct geographical regions. Clade A contained the haplotypes found mostly in individuals from the Tianshan Mountains area. Clade B contained haplotypes from populations located in other deserts in northern China. The divergence times indicated that the history of the M. meridianus complex was influenced by the uplift of the Tianshan Mountains and climate‐induced habitat fluctuations. In the Pleistocene, the expansion of forests and grasslands during interglacial period led to the isolation of the M. meridianus complex, which preferred to inhabit deserts. Hence, long geological isolation and the M. meridianus complex adaptation to local ecological conditions led to its genetic divergence. Clade A had long‐lasting demographic stability, most likely because the populations of this clade remained in a stable desert environment for a long time. However, the extension of other deserts and disappearance of palaeolakes during the last glacial period resulted in demographic expansion of Clade B. Furthermore, our genetic data indicated that two subspecies may exist within the M. meridianus complex. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 362–383.     

A new cryptic species of Aphaenops (Coleoptera: Carabidae: Trechinae) from a French Pyrenean cave: Congruence between morphometrical and geographical data confirm species isolation

A new species of cave-dwelling beetle from the pyrenean massif, Aphaenops (Cerbaphaenops) jauzioni n. sp. (Coleoptera: Carabidae), is described. Geometric morphometric analyses based on five morphological structures and comparisons with two populations of the closely related species Aphaenops (Cerbaphaenops) cerberus Dieck 1869 support the uniqueness of the new species. The specific status of the new taxon is also confirmed by the male genitalia structures. A putative scenario of population isolation is proposed.     

EVOLUTIONARY INFERENCES FROM THE ANALYSIS OF EXCHANGEABILITY

Evolutionary inferences are usually based on statistical models that compare mean genotypes or phenotypes (or their frequencies) among populations. An alternative is to use the full distribution of genotypes and phenotypes to infer the “exchangeability” of individuals among populations. We illustrate this approach by using discriminant functions on principal components to classify individuals among paired lake and stream populations of threespine stickleback in each of six independent watersheds. Classification based on neutral and nonneutral microsatellite markers was highest to the population of origin and next highest to populations in the same watershed. These patterns are consistent with the influence of historical contingency (separate colonization of each watershed) and subsequent gene flow (within but not between watersheds). In comparison to this low genetic exchangeability, ecological (diet) and morphological (trophic and armor traits) exchangeability was relatively high—particularly among populations from similar habitats. These patterns reflect the role of natural selection in driving parallel adaptive changes when independent populations colonize similar habitats. Importantly, however, substantial nonparallelism was also evident. Our results show that analyses based on exchangeability can confirm inferences based on statistical analyses of means or frequencies, while also refining insights into the drivers of—and constraints on—evolutionary diversification.     

DEGREE OF SYMPATRY AFFECTS REINFORCEMENT IN DROSOPHILA

In a recent paper, Yukilevich (2012) showed that asymmetries between Drosophila species in the strength of premating isolation tend to match asymmetries in the costs of hybridization (inferred from asymmetries in the strength of postzygotic isolation and range sizes). The results provide novel evidence that the outcome of reinforcement can depend on the strength and frequency of selection against hybridization. Here, I reanalyze the data to demonstrate that another (unconsidered) factor, namely the quantitative degree of sympatry between species, also predictably affects reinforcement. Specifically, premating isolation is strongest at intermediate degrees of sympatry. This result complements, rather than challenges, those of Yukilevich (2012) . One possible explanation for this newly discovered pattern is that when the degree of sympatry is small, selection for avoidance of hybridization is rare, but when the degree of sympatry is large, homogenizing gene flow overcomes reinforcing selection. Thus, reinforcement may depend on the balance between selection and gene flow. However, the current work examined degree of sympatry, not gene flow itself. Thus, further data on gene flow levels in Drosophila is required to test this hypothesis, which emerged from the patterns reported here.     

CORRELATION BETWEEN ANOLIS LIZARD DEWLAP PHENOTYPE AND ENVIRONMENTAL VARIATION INDICATES ADAPTIVE DIVERGENCE OF A SIGNAL IMPORTANT TO SEXUAL SELECTION AND SPECIES RECOGNITION

Although the importance of signals involved in species recognition and sexual selection to speciation is widely recognized, the processes that underlie signal divergence are still a matter of debate. Several possible processes have been hypothesized, including genetic drift, arbitrary sexual selection, and adaptation to local signaling environments. We use comparative analyses to investigate whether the remarkable geographic variation of dewlap phenotype in a Hispaniolan trunk Anolis lizard (A. distichus) is a result of adaptive signal divergence to heterogeneous environments. We recover a repeated pattern of divergence in A. distichus dewlap color, pattern, and size with environmental variation across Hispaniola. These results are aligned with ecological models of signal divergence and provide strong evidence for dewlap adaptation to local signaling environments. We also find that A. distichus dewlaps vary with the environment in a different manner to other previously studied anoles, thus expanding upon previous predictions on the direction dewlaps will diverge in perceptual color space in response to the environment.     

GENETIC AND DEVELOPMENTAL BASIS OF F2 HYBRID BREAKDOWN IN NASONIA PARASITOID WASPS

Speciation is responsible for the vast diversity of life, and hybrid inviability, by reducing gene flow between populations, is a major contributor to this process. In the parasitoid wasp genus Nasonia, F₂ hybrid males of Nasonia vitripennis and Nasonia giraulti experience an increased larval mortality rate relative to the parental species. Previous studies indicated that this increase of mortality is a consequence of incompatibilities between multiple nuclear loci and cytoplasmic factors of the parental species, but could only explain ～40% of the mortality rate in hybrids with N. giraulti cytoplasm. Here we report a locus on chromosome 5 that can explain the remaining mortality in this cross. We show that hybrid larvae that carry the incompatible allele on chromosome 5 halt growth early in their development and that ～98% die before they reach adulthood. On the basis of these new findings, we identified a nuclear‐encoded OXPHOS gene as a strong candidate for being causally involved in the observed hybrid breakdown, suggesting that the incompatible mitochondrial locus is one of the six mitochondrial‐encoded NADH genes. By identifying both genetic and physiological mechanisms that reduce gene flow between species, our results provide valuable and novel insights into the evolutionary dynamics of speciation.