Speciation progress: a case study on the bushcricket Poecilimon veluchianus

Eweleit L, Reinhold K, Sauer J. Speciation progress: a case study on the bushcricket Poecilimon veluchianus. PLoS ONE. 2015;10(10): e0139494.Different mechanisms such as selection or genetic drift permitted e.g. by geographical isolation can lead to differentiation of populations and could cause subsequent speciation. The two subspecies of Poecilimon veluchianus, a bushcricket endemic to central Greece, show a parapatric distribution and are partially reproductively isolated. Therefore, P. veluchianus is suitable to investigate an ongoing speciation process. We based our analysis on sequences of the internal transcribed spacer (ITS) and the mitochondrial control region (CR). The population genetic analysis based on the nuclear marker ITS revealed a barrier to gene flow within the range of Poecilimon veluchianus, which corresponds well to the described subspecies. In contrast to the results based on the nuclear ITS marker, the mitochondrial CR marker does not clearly support the separation into two subspecies with restricted gene flow and a clear contact zone. Furthermore, we could identify isolation by distance (IBD) as one important mechanism responsible for the observed genetic structure (based on the ITS marker). The population genetic analysis based on the nuclear marker ITS also suggests the existence of hybrids in the wild. Furthermore, the simultaneous lack of strong prezygotic barriers and the presence of postzygotic mating barriers, observed in previous laboratory experiments, suggest that a secondary contact after an allopatric phase is more likely than parapatric speciation

Lack of support for Rensch's rule in an intraspecific test using red flour beetle (Tribolium castaneum) populations

Rensch's rule proposes a universal allometric scaling phenomenon across species where sexual size dimorphism (SSD) has evolved: in taxa with male‐biased dimorphism, degree of SSD should increase with overall body size, and in taxa with female‐biased dimorphism, degree of SSD should decrease with increasing average body size. Rensch's rule appears to hold widely across taxa where SSD is male‐biased, but not consistently when SSD is female‐biased. Furthermore, studies addressing this question within species are rare, so it remains unclear whether this rule applies at the intraspecific level. We assess body size and SSD within Tribolium castaneum (Herbst), a species where females are larger than males, using 21 populations derived from separate locations across the world, and maintained in isolated laboratory culture for at least 20 years. Body size, and hence SSD patterns, are highly susceptible to variations in temperature, diet quality and other environmental factors. Crucially, here we nullify interference of such confounds as all populations were maintained under identical conditions (similar densities, standard diet and exposed to identical temperature, relative humidity and photoperiod). We measured thirty beetles of each sex for all populations, and found body size variation across populations, and (as expected) female‐biased SSD in all populations. We test whether Rensch's rule holds for our populations, but find isometry, i.e. no allometry for SSD. Our results thus show that Rensch's rule does not hold across populations within this species. Our intraspecific test matches previous interspecific studies showing that Rensch's rule fails in species with female‐biased SSD.The authors further thank NERC (Standard research grant to MJGG, BCE and OYM), Swiss National Science Foundation (postdoctoral fellowships and Ambizione grants to OYM), the University of East Anglia and ETH Zürich for support.Peer Reviewe

Inferring speciation and gene flow: a case study in a Mediterranean bushcricket, Poecilimon veluchianus

Eweleit L. Inferring speciation and gene flow: a case study in a Mediterranean bushcricket, Poecilimon veluchianus. Bielefeld; 2016

Body size and elevation: do Bergmann's and Rensch's rule apply in the polytypic bushcricket Poecilimon veluchianus?

Eweleit L, Reinhold K. Body size and elevation: do Bergmann's and Rensch's rule apply in the polytypic bushcricket Poecilimon veluchianus? Ecological Entomology. 2014;39(1):133-136.1. One of the most fundamental differences between animals are size differences that are often prominent when comparing species, as well as the sexes within species. One important aim of evolutionary and ecological studies is therefore to understand the pattern of size variation. 2. Bergmann’s rule and Rensch’s rule are two ideas that describe such general patterns. But whether or not these rules apply only in homoeothermic animals, or also in insects, is unclear because previous studies have shown opposing results. 3. For two subspecies of Poecilimon veluchianus Ramme (Orthoptera: Tettigoni- idae), we demonstrate a pattern that is opposite to what is predicted by Bergmann’s rule. Rensch’s rule also does not seem to apply, as sexual size dimorphism (SSD) does not change even though body size decreases with elevation in these two taxa. Our data adds to an emerging pattern that the two rules are not universally applicable in insects

Fitness consequences of seasonally different life histories? A match–mismatch experiment

To survive and reproduce successfully, animals have to find the optimal time of breeding. Species living in nontropical environments often adjust their reproduction plastically according to seasonal changes of the environment. Information about the prevailing season can be transmitted in utero, leading to the adaptation of the offspring to the prevailing season. After birth, animals acquire additional personal information about the environment, which allows them to adjust their reproductive investment. Here, we tested in a full-factorial match–mismatch experiment the influence of reproductive adjustments according to maternal and personal information. We bred wild cavies (Cavia aperea), a precocial rodent, either into increasing (spring) or decreasing (autumn) photoperiod and, subsequently, after weaning, transferred female offspring to the matching or mismatching season. We measured growth, specific metabolic rate (sRMR) and reproductive events across six months. Although sRMR was elevated for females primed for good (spring) conditions when transferred to the mismatching autumn condition, we found no maternal effects on reproduction. Females adjusted their reproductive decisions according to the season they personally experienced, thereby implying a potentially high level of plasticity. Females reproducing in spring started reproduction earlier with a lower reproductive effort than females reproducing in autumn but, ultimately, the two groups did not differ in survival, growth, or reproduction. These data suggest important developmental plasticity, highlight the use of personal information acquired after weaning over early information provided until weaning, and point out the potential value of multiple cues, such as food abundance and quality and temperature besides photoperiod

Results of dbRDA for the calculated regions/partitions for the ITS marker.

<p>Results of dbRDA for the calculated regions/partitions for the ITS marker.</p

Distribution of shared and exclusive haplotypes of the ITS marker regarding to their frequencies, with hypothesized contact zone (dashed line).

<p>The Map was prepared in DIVA-GIS version 7.5.0.0 using an elevation shapefile freely available at <a href="https://research.cip.cgiar.org/gis/" target="_blank">https://research.cip.cgiar.org/gis/</a>.</p

Summary of Tajima D test and Fu’s and Li’s F* and D* test of the ITS dataset.

<p>Summary of Tajima D test and Fu’s and Li’s F* and D* test of the ITS dataset.</p

Genetic structure and diversity for the ITS marker, according to the new subspecies.

<p>Genetic structure and diversity for the ITS marker, according to the new subspecies.</p

Distribution of shared and exclusive haplotypes of the ITS marker regarding to their frequencies, with new contact zone (dashed line).

<p>The Map was prepared in DIVA-GIS version 7.5.0.0 using an elevation shapefile freely available at <a href="https://research.cip.cgiar.org/gis/" target="_blank">https://research.cip.cgiar.org/gis/</a>.</p