PlasticitySpeciation · Phenotypic plasticity and speciation in cichlids
FP7 — People (Marie Curie Actions)
- Duration
- 2013-03-01 → 2015-02-28
- EU contribution
- €161,969
- Participants
- 1
- Scheme
- MC-IEF
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Results in brief
Phenotypic plasticity and speciation in cichlids
The aim of the project was to empirically test a set of expectations stemming from a body of theoretical work on the impact of phenotypic plasticity – i.e. the ability of a single genotype to produce different phenotypes in different environments – on diversification and speciation. According to this previous work, when in the presence of a trade-off, a phenomenon called “genetic assimilation” is expected. This is a process whereby an environmentally induced phenotype becomes canalized through selection acting upon the developmental system. The expected outcome when comparing the ancestral state to the state derived via genetic assimilation is a reduction in plasticity (i.e. the derived form has a smaller phenotypic change in response to an environmental stimulus). Midas cichlid fish are an ideal system to test such an hypothesis as derived species from a crater lake environment have diverged very rapidly from their ancestors from a tectonic lake environment. Due to this rapid divergence, both ancestral and derived forms are still present in Nicaraguan lakes and can be, then, subjected to experimental manipulation. In this project broods of the two species Amphilophus citrinellus (ancestral species from Lake Nicaragua) and A. zaliosus (derived species from Lake Apoyo) were produced from wild-caught, lab-reared fish currently hosted in the University of Konstanz animal facilities (TFA). They were raised and, then, subjected to the differential food treatment (hard diet/soft diet). From the digital photographs of the pharyngeal jaws of the treatment and control groups, Dr. Fruciano digitized a set of 12 points. After generalized Procrustes analysis, the allometric variation was removed by multivariate regression of shape variables on body centroid size. Based on this data now corrected for allometry, Dr. Fruciano tested for differences in pharyngeal jaw shape between treatment and control groups and visualized their differences in means. The main message is that the difference in means in A. zaliosus between treatment and control is lower than the one in A. citrinellus, suggesting lower levels of plasticity in the derived species. This agrees well with the theory and anticipated results as outlined in the original proposal.
Data: CORDIS, © European Union
Project objective
Phenotypic plasticity is considered a catalyst for speciation through two alternative mechanisms: the Baldwin effect and genetic assimilation. Midas cichlids – Nicaraguan freshwater fishes where multiple species diverged in sympatry in crater lakes after colonization from larger source lakes – are the ideal model to study the influence of plasticity in speciation. The presence of trade-offs in the morphology of Midas cichlids’ pharyngeal jaw – a trophic structure used to crush hard food items which plastically modifies its size and shape when subjected to hard food – allows to generate specific hypotheses. In fact, according to theoretical models, in presence of trade-offs genetic assimilation is more likely than the Baldwin effect. I will use common garden experiments involving two Midas species from Lake Apoyo and the species from Lake Nicaragua (which acted as a source for Lake Apoyo) subjecting the fish to hard and soft diet treatments, that are nutritionally identically and only differ in their hardness. I will then measure the levels and directions of plastic response in each species/treatment using advanced geometric morphometric analyses and I will assess their transcriptional correlates using a combination of Illumina RNA next generation sequencing and RT-qPCR. I will, therefore, be able to test the following three hypotheses: 1. that the derived populations from Lake Apoyo show lower levels of plasticity than source species (as expected as a consequence of genetic assimilation); 2. that the plastic response in the source population produces the same phenotypes found in natural populations of the derived species (as expected according to the “flexible stem hypothesis”); 3. comparing the results with published data from African cichlids, that the genes differentially expressed in pharyngeal jaw plastic response are the same in both closely and distantly related cichlid lineages (thus suggesting a conserved molecular basis for pharyngeal jaw plasticity).
Original text from CORDIS.
Participants
- UNIVERSITAT KONSTANZ · KonstanzCoordinatorGermany
Links
Data: CORDIS, © European Union