The use of nuclear and mitochondrial single nucleotide polymorphisms to identify cryptic species

There is growing interest in the use of single nucleotide polymorphisms for evolutionary and population genetics. We tested the efficacy of one of the available single nucleotide polymorphism techniques, single-base extension, in distinguishing four cryptic species of Microtus. Sequence data were available for these species at nuclear and mitochondrial loci and their identity could be independently confirmed using karyotypes. We found that the development and optimization of single nucleotide polymorphisms required extensive effort, and that the method accurately identified the correct nucleotide at single nucleotide polymorphism sites approximately 90% of the time at the conserved nuclear locus. Correct identification rates were much lower at the highly variable mitochondrial locus.     

Edaphic races and phylogenetic taxa in the Lasthenia californica complex (Asteraceae: Heliantheae): an hypothesis of parallel evolution

Lasthenia californica sensu Ornduff consists of two races that differ in their flavonoid pigments and edaphic tolerances. Recent phylogenetic studies of Lasthenia have revealed that members of L. californica sensu Ornduff belong to two phylogenetic species. The relationship of the edaphic races to these new species and to each other is the focus of this study. Characterization of flavonoid profiles and phylogenetic placement of 33 populations demonstrates that races and phylogenetic taxa are not concordant, suggesting that one or both edaphic races evolved in parallel in the two clades. We hypothesize an edaphically linked ecological role for flavonoid differences that first revealed the existence of two races.     

Determinants of sperm transfer in the scorpionfly Panorpa cognate: male variation, female condition and copulation duration

Recent studies suggest that sperm production and transfer may have significant costs to males. Male sperm investment into a current copulation may therefore influence resources available for future matings, which selects for male strategic mating investment. In addition, females may also benefit from actively or passively altering the number of sperm transferred by males. In the scorpionfly Panorpa cognata, the number of sperm transferred during copulation depended on copulation duration and males in good condition (residual weight) copulated longer and also transferred more sperm. Moreover, sperm transferred and stored per unit time was higher in copulations with females in good condition than in copulations with females in poor condition. Males varied greatly and consistently in their sperm transfer rate, indicative of costs associated with this trait. The duration of the pairing prelude also varied between males and correlated negatively with the male's sperm transfer rate, but no other male character correlated significantly with male sperm transfer rate. The results are consistent with strategic mating effort but sperm transfer could also be facilitated by the physical size of females and/or females in good condition may be more cooperative during sperm transfer.     

The evolution of polyandry: patterns of genotypic variation in female mating frequency, male fertilization success and a test of the sexy-sperm hypothesis

The sexy-sperm hypothesis predicts that females obtain indirect benefits for their offspring via polyandy, in the form of increased fertilization success for their sons. I use a quantitative genetic approach to test the sexy-sperm hypothesis using the field cricket Teleogryllus oceanicus. Previous studies of this species have shown considerable phenotypic variation in fertilization success when two or more males compete. There were high broad-sense heritabilities for both paternity and polyandry. Patterns of genotypic variance were consistent with X-linked inheritance and/or maternal effects on these traits. The genetic architecture therefore precludes the evolution of polyandry via a sexy-sperm process. Thus the positive genetic correlation between paternity in sons and polyandry in daughters predicted by the sexy-sperm hypothesis was absent. There was significant heritable variation in the investment by females in ovaries and by males in the accessory gland. Surprisingly there was a very strong genetic correlation between these two traits. The significance of this genetic correlation for the coevolution of male seminal products and polyandry is discussed.     

Interspecific and intraspecific differences in two Liriomyzaleafminer species in California

In recent years, the pest status of Liriomyza trifolii (Burgess) and L. huidobrensis (Blanchard) (Diptera: Agromyzidae) has changed in California, as well as other areas of the world. In California, L. huidobrensis has become the predominant Liriomyza species in valleys along the central coast, while L. trifolii remains the predominant species in southern California. To investigate possible reasons for this change in status, differences in host plant use and reproductive success of intraspecific populations were examined for Liriomyza trifolii and L. huidobrensis from both central and southern California. The southern L. trifolii fed, oviposited and reproduced successfully on all five hosts tested, but the central population fed significantly less on all hosts and was restricted to reproducing on pepper only. With the exception of pepper, southern L. trifolii had significantly greater larval survival on all hosts than central L. trifolii. In contrast, the central L. huidobrensis population had greater reproductive success than the southern population of that species on all hosts plants tested. However, pepper was not a suitable host for either L. huidobrensis population. Both species showed positive assortative mating, with homotypic mating occurring more frequently than heterotypic mating; however, the difference between L. trifolii populations was much more pronounced than between L. huidobrensis populations. These data indicate that central and southern California populations of each species are distinct biotypes. Furthermore when coupled with previous genetic data, our results suggest the possible existence of cryptic species within L. trifolii.     

Patterns of divergence in the effects of mating on female reproductive performance in flour beetles

Sexual selection can lead to rapid divergence in reproductive characters. Recent studies have indicated that postmating events, such as sperm precedence, may play a key role in speciation. Here, we stress that other components of postmating sexual selection may be involved in the evolution of reproductive isolation. One of these is the reproductive investment made by females after mating (i.e., differential allocation). We performed an experiment designed to assess genetic divergence in the effects of mating on female reproductive performance in flour beetles, Tribolium castaneum. Females were mated to males of three different wild-type genotypes at two different frequencies, in all possible reciprocal combinations. Male genotype affected all aspects of female reproduction, through its effects on female longevity, total offspring production, reproductive rate, mating rate, and fertility. Moreover, male and female genotype interacted in their effects on offspring production and reproductive rate. We use the pattern of these interactions to discuss the evolutionary process of divergence and suggest that the pattern is most consistent with that expected if divergence was driven by sexually antagonistic coevolution. In particular, the fact that females exhibited a relatively weak response to males with which they were coevolved suggests that females have evolved resistance to male gonadotropic signals/stimuli.     

Phylogeographic analysis of the brooding brittle star Amphipholis squamata (Echinodermata) along the coast of New Zealand reveals high cryptic genetic variation and cryptic dispersal potential

Abstract.— Direct development in benthic marine invertebrates is usually associated with narrow geographical range, low rates of colonization, and low levels of gene flow. Paradoxically, the small brittle star Amphipholis squamata broods its larvae to a crawl-away juvenile stage, yet has a cosmopolitan distribution. Using sequence and restriction-fragment-length-polymorphisms (RFLP) analyses of nuclear and mitochondrial DNA from 16 coastal populations throughout New Zealand, we tested whether the species is indeed a poor disperser, as may be expected from its brooding habit. We predicted that local and regional populations would be genetically structured according to isolation by distance. We also suspected that this ubiquitous "species" is composed of a variety of cryptic taxa in different geographic areas, as has been discovered in an increasing number of marine invertebrates. We found evidence of four genetically divergent and reproductively isolated lineages that can exist in syntopy. Lineages vary in abundance, haplotype diversity, and geographic distribution. The partitioning of genetic variation within the most common lineage, as well as the geographic distribution of the four lineages, suggest a north/south split. This pattern is consistent with known New Zealand marine biogeographic zones and appears to be linked to the regime of oceanic circulation, which is characterized by subtropical, southward-moving water masses in the north, and sub-Antarctic, northward-moving water in the south. We conclude that the dispersal ability of A. squamata is regionally restricted but with sporadic long-distance dispersal, which serves to increase local genetic variation. Our results support the idea that dispersal occurs through passive transport by drifting or rafting on macroalgae, which A. squamata commonly inhabits, and emphasize that poor dispersal ability is not necessarily a corollary of direct development.     

Morphological analysis of three equivocal sibling species of Deprea (Solanaceae)

Taxonomic confusion among closely related and morphologically similar Deprea species has persisted in the literature and in the identification of species. Morphological variation among three closely related, monophyletic Deprea species was studied to determine if and how they can be distinguished. Their sympatric occurrence in Venezuela afforded an opportunity to couple field study with analysis of herbarium specimens representing their entire geographic range. An analysis of 94 morphological characters resulted in five vegetative and 13 reproductive taxonomically informative traits. Canonical variates analysis clearly separated the three species using six quantitative traits. We conclude that these taxa, although quite variable and similar morphologically, are taxonomically distinct. Results of character analysis indicated that D. orinocensis is morphologically more similar to D. bitteriana than either are to D. paneroi. In D. paneroi, small, sterile anthers on fruit-bearing plants and the absence of fruits on plants possessing large, plllen-bearing anthers, suggest cryptic dioecy. Based on these data, D. granulosa is considered to be a synonym of D. orinocensis: Athenaea bitteriana, a misapplied synonym, is the correct basionym and is applicable to many specimens identified as D. granulosa. We submit a new combination, D. bitteriana (Werderm.) Sawyer & Benítez, and designate a lectotype to accommodate these findings.     

Mitochondrial DNA variation and the evolutionary history of the Mediterranean species of Cicada L. (Hemiptera,Cicadoidea)

Cicadas are widely distributed in the Mediterranean area and are mainly distinguished by male acoustic signals, which act as specific mate recognition systems. Within the genus Cicada L. several species have diverged in their calling songs without showing external morphological differences, so acoustic recordings and genetic studies are particularly useful for systematic, biogeography and evolutionary studies. This study assesses sequence variation in closely related species of Cicada from the Mediterranean area, using domain III of the 12S rRNA mitochondrial gene in order to determine the phylogenetic relationships and the evolutionary history of this group, as well as the population structure of the two most common species, C. orni and C. barbara. Five distinct haplogroups were identified, C. orni, C. barbara, C. mordoganensis, C. cretensis and C. lodosi, each corresponding to a distinct evolutionary group. C. barbara was the most divergent species within this group, while C. orni and C. mordoganensis were the most similar. The population structure and demographic parameters of the species were not completely resolved. However, there is evidence for the separation of the C. orni Greek populations from the rest of Europe and also for demographic expansions probably related to Pleistocene climate changes. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 266–288.     

Interplay of host specificity and biogeography in the population structure of a cosmopolitan endoparasite: microsatellite study of Ligula intestinalis (Cestoda)

Organisms with wide geographical or phenotypic diversity often constitute assemblages of genetically distinct species or lineages. Within parasites, an emergence of host-specific lineages is assumed to create such cryptic variability; however, empirical evaluation of these processes is scarce. Here, we analyse populations of a parasite with a complex life cycle, wide host spectrum and global distribution, with the aim to reveal factors underlying the evolution of host- or geography-dependent lineages. Using 15 microsatellite loci, deep genetic distances were observed between populations from distant geographical areas. On the local scale, host-mediated genetic structure was found among sympatric samples. Two lineages differing in the spectrum of infected hosts co-occurred in the Euro-Mediterranean area, and two distinct lineages were recovered from Lake Tana in Ethiopia. Although sampled across several host taxa and multiple localities, a lack of marked genetic structure was seen in the populations belonging to one of the European lineages. Only weak genetic differentiation between sympatric samples from two host species was found. Complexity of the parasite life-cycle contributed to such a stratified pattern. Differences in the immune response between fish hosts were suggested as the factor diversifying the populations locally; conversely, high mobility of the parasite due to migration with its bird (definitive) host were assessed to homogenize populations across the area of distribution. However, despite the high mobility, large bodies of salt water prevent the parasite from long-distance migrations, as was demonstrated in an example of the Mediterranean Sea which represented an effective barrier to gene flow.