Environmental differences can cause reproductive isolation to evolve. Distinct habitats can be particularly important for the evolution of genetically based sexual isolation, which occurs when divergent preferences and mating traits... more
Environmental differences can cause reproductive isolation to evolve. Distinct habitats can be particularly important for the evolution of genetically based sexual isolation, which occurs when divergent preferences and mating traits reduce mating between species. Yet, we know little about environmental effects on the potentially plastic expression, and thus the current maintenance, of sexual isolation. This is especially intriguing in the context of reverse speciation, where previously isolated taxa begin hybridizing and merge. Environmental change could weaken reproductive isolation underlain by plastic traits even before any genetic change occurs. Here, we examine how differences in mating habitats affect the expression of both female discrimination between species and male traits that underlie sexual isolation. We used 2 species pairs of threespine stickleback fish (Gasterosteus spp.): an intact species pair and a formerly distinct but now hybridizing species pair, where habitat change presumably triggered reverse speciation. The expression of female discrimination was fairly insensitive to habitat, despite the central importance of habitat differences to the initial evolution of sexual isolation. Only the ecotype being subsumed by hybridization showed habitat sensitivity, suggesting this plasticity may have contributed to reverse speciation either as a cause or consequence of gene flow. Also, we found plasticity in male courtship across habitats that could further erode sexual isolation. Thus, environmental differences may play different roles in the genetic evolution versus plastic maintenance of sexual isolation, with implications for the forward versus reverse processes of speciation.
Many helminth parasites have evolved strategies to evade the immune response of their hosts, which includes immunomodulation. Prostaglandin E2 (PGE2) is one of the best-described immunomodulators in mammalian helminth parasite infections.... more
Many helminth parasites have evolved strategies to evade the immune response of their hosts, which includes immunomodulation. Prostaglandin E2 (PGE2) is one of the best-described immunomodulators in mammalian helminth parasite infections. We hypothesized that also in teleost fish anti-helminthic immune responses are regulated via PGE2. We used a model system consisting of the tapeworm Schistocephalus solidus and its host, the three-spined stickleback (Gasterosteus aculeatus), to investigate in vitro effects of PGE2 on head kidney leucocytes (HKL) derived from sticklebacks that were experimentally infected with S. solidus. PGE2 was tested alone or in combination with either S. solidus antigens or bacterial lipopolysaccharides (LPS). After in vitro culture, cell viability and changes in leucocyte subpopulations (granulocytes to lymphocytes ratios) were monitored by flow cytometry and HKL were tested for their capacity to produce reactive oxygen species (ROS) with a chemiluminescence assay. In short term (2 h) HKL cultures PGE2 did not change the total numbers of live HKL, but the production of ROS decreased significantly with high (0.1 mmol L1) PGE2 concentrations. In long-term (96 h) cultures high PGE2 concentrations induced a sharp decrease of leucocytes viability, while low (0.1 pmol L1) and intermediate (0.1 nmol L1) concentrations of PGE2 caused elevated leucocyte viability compared to controls. This coincided with reduced ROS production in cultures with high PGE2 and elevated ROS production in cultures with low PGE2. Granulocyte to lymphocyte ratios increased with high PGE2 concentrations alone and in combination with S. solidus antigens and LPS, most prominently with HKL from S. solidus infected sticklebacks. The present study supports the hypothesis that PGE2 might be an immunomodulator in tapewormefish parasiteehost interactions.
We compared the colour patterns of free swimming, reproductively active male threespine stickleback Gasterosteus aculeatus of the anadromous and stream ecotypes from three geographically distinct regions. Consistent with the hypothesis of... more
We compared the colour patterns of free swimming, reproductively active male threespine stickleback Gasterosteus aculeatus of the anadromous and stream ecotypes from three geographically distinct regions. Consistent with the hypothesis of environmentally mediated selection , our results indicate ecologically replicated differences in G. aculeatus coloration between anadromous and stream-resident populations, and that G. aculeatus probably have the visual acuity to discriminate colour pattern differences between anadromous and stream-resident fish.
One approach to understand the importance of reproductive barriers to the speciation process is to study the breakdown of barriers between formerly distinct species. One reproductive barrier, sexual isolation, reduces gene flow between... more
One approach to understand the importance of reproductive barriers to the speciation process is to study the breakdown of barriers between formerly distinct species. One reproductive barrier, sexual isolation, reduces gene flow between species through differences in mate preferences and mating signals and is likely important for species formation and maintenance. We measure sexual isolation in two limnetic-benthic threespine stickleback species pairs (Gasterosteus spp.). One species pair maintains strong reproductive isolation while the other species pair has recently collapsed into a hybrid swarm. We compare the strength of sexual isolation in the hybridizing pair to the currently isolated pair. We provide the first evidence that sexual isolation has been lost in the hybridizing pair and show furthermore that preferences females have for conspecific mates and the traits they use to distinguish conspecific and heterospecific males contribute to this loss. This work highlights the fragility of reproductive isolation between young species pairs and considers the role of sexual isolation in speciation [Current Zoology 59 (5): 591−603, 2013].
