Entamoeba varieties use biochemical signaling and behavioral aggregation to discriminate between members of distinctive strains
Author(s): Espinosa, A, Paz-y-Miño-C, G
Evolutionary processes in which selection acted continuously and cumulatively on ancestors of Entamoeba populations gave rise to chemical and behavioral signals that allowed individuals to discriminate non-population members and, gradually, to the emergence of new lineages. The concept of ‘species recognition’ at the unicellular level might be artificial and inadequate to define signaling in single-cell natural populations. Aggregative behavior could be explored in a nonsocial protist to define discrimination cues among/between natural varieties. We demonstrate that by color tagging and pair-mix-culturing six Entamoeba varieties, the difficulty of discerning among apparently similar taxa can be resolved. When grown together with different amoeba strains, free-living/opportunistic (E. moshkovskii Laredo), commensal (E. moshkovskii Snake) or parasitic (E. invadens IP-1, E. invadens VK-1:NS, E. terrapinae, E. histolytica) trophozoites aggregate only with members of their own lineage. Clusters of trophozoites from each amoeba show distinctive rate of aggregation, density of cells per cluster, and distance between clusters. By using these behavioral cues, and identifying the genes involved in cell-signaling for cluster formation, distinctive amoeba taxa can be characterized quantitatively; we postulate that not only Entamoeba varieties, but apparent taxa crypticity in other protists, can be resolved by examining the natural ability of unicellular eukaryotes to discriminate between members and non-members of a lineage. Thus, phylogenetic relations among protists, which are usually determined by morphology and molecular techniques (the latter often confounded by horizontal gene transfer), could be further understood by incorporating behavior into the evolutionary analysis of this complex group of organisms.
Natural History Museum
An experimental test of a potential post-copulatory pre-zygotic reproductive barrier in a passerine species pair
Author(s): Cramer, ERA, Laskemoen, T, Eroukhmanoff, F, Haas, F, Hermansen, JS, Lifjeld, JT, Rowe, M, Sætre, G, Johnsen, A
Sexual selection may drive speciation, but most research has focused only on pre-copulatory sexual selection, overlooking post-copulatory processes. Under strong post-copulatory sexual selection, post-copulatory pre-zygotic (PCPZ) phenotypes could diverge, limiting gene flow upon secondary contact. We did in vitro experiments on a potential PCPZ barrier between sister species: house sparrows (Passer domesticus) and Spanish sparrows (P. hispaniolensis). In birds, sperm selection most likely occurs as sperm cross the vagina, so we tested if reproductive tract fluid of heterospecific females reduced sperm swimming speed or motility, relative to conspecific female fluid. We found that house sparrow female fluids affected the two species’ sperm asymmetrically, consistent with the observed asymmetrical genetics of the hybrid species, the Italian sparrow (P. italiae, which has house sparrow mitochondrial DNA but mixed house and Spanish sparrow nuclear DNA). In house sparrow female fluid, slow-swimming house sparrow sperm were sped up, and fast-swimming house sparrow sperm were slowed down. Spanish sparrow sperm was not systematically affected, thereby increasing the speed difference between fast-swimming Spanish sparrow sperm and randomly-chosen house sparrow sperm. This could contribute to asymmetrical introgression if Spanish sparrow males with fast-swimming sperm are also more likely to seek extra-pair copulations, which is plausible. Overall, however, there was no evidence for a PCPZ barrier: sperm performed equally in conspecific and heterospecific female fluids, and the species had similar sperm morphology, sperm swimming performance, and female fluid protein profiles. Low divergence in PCPZ phenotypes between species may be insufficient to cause an overall PCPZ barrier, and may be due to low post-copulatory sexual selection within each species. Also, pre-copulatory barriers between the species may prevent PCPZ barriers from evolving via reinforcement.
Department of Animal biology
Asymmetric reproductive interference among two spider mite species
Author(s): Clemente, SGLH, Rodrigues, L, Ponce, AR, Cruz, C, Magalhães, S
Incomplete specific recognition can lead to the occurrence of reproductive interference (RI) - reproductive interactions between two species resulting in fitness loss for at least one of them. RI can play an important role in the coexistence of species, being especially important in the fate of introduced exotic species and in pest management.Tetranychus urticae and Tetranychus evansi are two closely related haplodiploid spider mite species that often coexist in solenaceous crops. Incomplete specific recognition occurs among these species: heterospecific matings were observed, although no hybrid progeny has been found. We tested two possible RI mechanisms: (1) the effect of mating with heterospecifics on virgin (haploid) offspring and (2), the consequences of heterospecific crosses for the offspring of females that have or will mate with conspecifics. Behavioural assays showed that (1) only T. urticae females and T. evansi males prefer to mate with conspecifics; (2) regarding latency to copulation individuals behave as virgins after mating heterospecifically, (3) T. urticae females copulate for a shorter period with heterospecifics than with conspecifcs. Results for fecundity and sex-ratio revealed that (1) for both species, fecundity of females mated with heterospecifics are similar to that of virgins - heterospecific crosses do not affect egg viability; (2) T. evansi females that mate with both conspecific and heterospecific males had higher fecundity than females that mated with a conspecific male only; this was not observed in T. urticae. (3) T. urticae females that mate with a heterospecific male after a conspecific mating had a lower percentage of female offspring. The results obtained point to the occurrence of asymmetric RI, in which T. evansi females benefits from mating with heterospecifics, whereas T. urticae pay a cost of such matings. These results may affect the coexistence of these species, a hypothesis requiring further testing.
Department of Animal Ecology
Does incorporation of alarm calls into avian song increase rates of signal divergence across species?
Author(s): Wheatcroft, D, Price, TD
Assortative mating of co-occurring species depends on the interaction between the evolution of signals involved in mating decisions and the corresponding recognition mechanisms. In two hybridizing Ficedula flycatcher species, both plumage characteristics and mate preferences are found on the paternally inherited Z chromosome, suggesting that assortative mating is achieved in these species through physical linkage of signals and preferences. In flycatchers, as in other songbird species, song functions not only in mate attraction, but also in interactions between males and has a learned component, leading to a series of potential problems for genetic linkage and assortative mating. Here, through experimental playbacks to Ficedula chicks from each species still in the nest, I show that chicks respond more strongly to the songs of their genetic fathers, suggesting that recognition of complex vocal signals is determined by genes on the Z chromosome. In contrast, chicks respond readily to the innately produced alarm calls of the other species, suggesting that recognition of vocal signals is achieved through mechanisms that are independent from how they are transmitted.
Department of Environmental Sciences
Ecological and molecular cues for colour change in a marine fish
Author(s): Cortesi, F, Cheney, KL, Marshall, JN, Salzburger, W
Coral reef fish are among the most colourful and beautifully patterned organisms on the planet; however, understanding the function and evolution of such coloured visual signals is unclear. Possible ways in which we can start to unlock the processes that have created such diversity in colours and patterns is to understand: 1) the molecular capacities that allow signal emergence, 2) how such visual signals are perceived by others (predators, competitors and potential mates), and 3) how this drives the evolution of such signals. To address these questions we are currently using the coral reef fish Pseudochromis fuscus as a model system. It is a species that exhibits multiple colour morphs, has the ability to change colouration between morphs, and is considered a putative aggressive mimic. However, the environmental cues that drive and the molecular basis that enable the species to change colour remain unclear. To investigate these questions we are using a multidisciplinary approach by combining behavioural, neurophysiological, cell histological and molecular methodologies. First results indicate mimicry as the main trigger for colour change in Pseudochromis fuscus. However, other benefits such as cryptic and predatory advantages might be associated with colour differences in this species. Ultimately we aim to better understand how colourful signals evolve, what kind of selective pressures might act on them and whether there are molecular similarities between the signal co-evolution of mimic and model species.
School of Biology
Effect of Wolbachia infection on the courtship song of Drosophila paulistorum and D. equinoxialis
Author(s): Vigoder, FM, Schneider, DI, Ritchie, MG, Miller, WJ
Understanding the processes that can lead to speciation are one of the main goals in evolutionary biology. It has been proposed that coevolution between parasite and its host can potentially drive speciation. A good model for studies of infectious speciation is the neotropical fly Drosophila paulistorum spp.. This species complex is currently under incipient speciation in nature and consists of six semispecies that are in an obligatory mutualistic relationship with bacteria of the Wolbachia genus. Previous studies have determined that infection with Wolbachia is associated with hybrid inviability and male sterility. Interesting enough, Wolbachia not only cause postzygotic isolation in the D. paulistorum complex but also prezygotic isolation through an influence on assortative mating between the different semispecies. These data suggest that the infection is modulating some courtship signal that allows self-recognition among the semispecies. Among the different male signals involved in mate recognition in Drosophila species, courtship song is one of the most studied and is well known to affect isolation between close related species. Here we recorded the courtship song of males from three D. paulistorum semispecies and also of its sibling species D. equinoxialis comparing wild type infected lines with lines treated with antibiotics where the bacteria titer were reduced. Our result shows a significant variation in the interpulse interval (IPI) associated with the infection with Wolbachia in all groups. We discuss whether the changes are likely to influence sexually selection or are more likely to reflect changes in male condition following curing of the Wolbachia infection.
Evolution of acoustic and visual signals in Asian barbets
Author(s): Gonzalez-Voyer, A, Castelló, A, Leonard, J
The study of animal communication systems is an important step towards gaining greater understanding of the processes influencing diversification because signals often play an important role in mate choice and can lead to reproductive isolation. Signal evolution can be influenced by a diversity of factors such as biophysical constraints on the emitter, the signalling environment, or selection to avoid heterospecific matings. Furthermore, because signals can be costly to produce, trade-offs may exist between different types of signals. Here, we apply phylogenetic comparative analyses to study the evolution of acoustic and visual signals in Asian barbets, a clade of non-Passerine, forest-dependent birds. Our results suggest that evolution of acoustic and visual signals in barbets is influenced by diverse factors, such as morphology and signalling environment, suggesting a potential effect of sensory drive. We found no trade-offs between visual and acoustic signals. Quite to the contrary, more colourful species sing significantly longer songs. Song characteristics presented distinct patterns of evolution. Song frequency diverged early on and the rate of evolution of this trait appears to be constrained by body size. On the other hand, characteristics associated with length of the song presented evidence for more recent divergence. Finally, our results indicate that there is a spatial component to the evolution of visual signals, and that visual signals are more divergent between closely related taxa than acoustic signals. Hence, visual signals in these species could play a role in speciation or reinforcement of reproductive isolation following secondary contacts.
Institut des Sciences de l'Evolution
From sexual communication to species recognition: examples from the house mouse
Author(s): Ganem, G
Sexual communication involves transfer of information between potential mates on their identity, quality, compatibility and history. Both endogenous and exogenous factors are expected to shape the evolution of the complex systems made of signals, receptors and preferences. Further, variation in the latter factors could result in divergence between the sexes, populations and species. How potential mates make sense of the diverse information available for mate choice remains an unresolved question. My research addresses this question in rodent species using the olfactory chemosensory channel to communicate. For example, several pheromones involved in social and sexual communication have been described in the house mouse (Mus musculus domesticus). These chemical cues are mostly present in the mouse urine and the mouse marks its territory by depositing urine drops. Moreover, mice are both excellent noses and carry odor signatures that act as fingerprints. Still, despite of this remarkable individual variability population and species differences exist. The house mouse is involved in chromosomal diversification in parts of its range and share a hybrid zone with another subspecies (M. m. musculus) along a north south axis crossing Europe from Scandinavia to the Black sea. Using these different evolutionary and geographical settings, research in my laboratory has addressed the mechanisms involved in mate recognition system divergence. Referring to examples from my research I shall illustrate how genetic drift, local adaptation sexual selection and reproductive interference shape the house mouse mate recognition system and could facilitate speciation.
Department of Biology
How can a sexually selected exaggerated male trait be reduced or lost?
Author(s): Jones, JC, Weber, M, Henning, F, Schartl, M, Meyer, A
What drives the evolution of male specific conspicuous traits? Sexual selection is known to act via female preference for exceptional traits. However, using phylogenomic (RAD sequencing) analysis we have shown that a definitive example of such a trait, the exaggerated caudal fin (or sword) specific to Xiphophorus fish, is likely to have been lost during the evolutionary history of this genus. If such a trait is subject to strong sexual selection, how can it be lost? To address these questions we used the green swordtail fish, Xiphophorus hellerii, whose sword is a textbook example of female association preferences. Classic studies have demonstrated through association tests that females prefer males with long swords, and even species whose males lack this trait prefer males with an artificial sword over their own non-sworded males. Here, we extend these findings by using a natural population setting, where males and females could freely interact and choose mates, to show that female preferences are highly likely to involve an array of male traits. By conducting independent replicate experiments we find no significant difference in paternity success between long and short sworded males, and in any given replicate females tended to choose the same male. Further, by genotyping sperm stored in the female ovary we provide the first indication that post-copulatory sexual selection may play a role in the paternity success of different males. Previous studies have largely painted a picture of the sword as the main determiner of reproductive success. Under this scenario, the repeated loss of the sword is paradoxical. By considering male sexiness as a more multivariate trait these losses can be explained by changes in the environment and fluctuations in population size.
Department of Sciences
Innate sex recognition and learned species recognition in an invasive fish
Author(s): Magellan, K
Sex and species recognition are both fundamental to sexual reproduction. Speciation imposes modification of species recognition traits but not necessarily those for sex recognition. However, most studies either focus on sex recognition characteristics in a single species or assume sex recognition a priori and focus solely on species recognition traits. Invasive species represent an ideal opportunity to explore the relationship between these two recognition systems. I investigated interactions between the highly invasive mosquitofish, Gambusia holbrooki and the native Iberian toothcarp, Aphanius iberus. I found that male Gambusia consistently differentiated between male and female heterospecifics but initially failed to distinguish heterospecific females from those of their own species. However, they began to learn to recognise species differences within 24 hours. Given the lack of costly mating displays and nuptial gifts in the mosquitofish mating system, sex recognition and misdirected mating attempts may be less costly than species recognition. This and their rapid learning ability may be a factor explaining the invasive success of G. holbrooki.