Sympatric speciation

Map of Nicaragua and sympatrically-speciating Midas cichlids from Fruciano et al. 2019 – Genome Biology and Evolution. Notice how benthic and limnetic species (diverged in sympatry) have different body shape. The inset presents a molariform and a papilliform lower pharyngeal jaws (typical of benthic and limnetic species, respectively)

Genetic mapping of adaptive traits in sympatrically-speciating Midas cichlids from Lake Apoyo (from Fruciano et al. 2016 – Nature Communications). a. The QTL regions for variation in body shape (orange), pharyngal jaw shape (aqua) and co-variation between these two traits (purple) overlap in a linkage group/chromosome (linkage group 3; note that other QTL were found in other linkage groups). b. and c. Body-pharyngeal jaw shape co-variation (c) and evidence of association with genetic variation in linkage group 3.

Sympatric speciation – the forming of two species in the same place and in the absence of physical barriers to gene flow – has been controversial for a long time. In fact, whether it was even possible has been a hotly debated topic for a long time.

Today, sympatric speciation is generally accepted as possible. The open question in current evolutionary biology is not, then, whether it is possible but how is it possible. That is, what are the conditions which allow or facilitate sympatric speciation?

I started working on this topic during my postdoc in Axel Meyer’s lab at the University of Konstanz (Germany).

There, I was able to work with one of the relatively few widely accepted cases of sympatric speciation: Midas cichlid fish from Nicaragua.

I approach this topic using an integrative approach, combining advanced morphometrics and genomics/transcriptomics.

• Is the genetic/genomic architecture of adaptive traits affecting the likelihood of sympatric speciation?
• What makes certain species able to speciate in sympatry when others won’t?

• The genetic non-independence of distinct adaptive traits may be contributing to speciation in sympatry
• The transcriptomes of Midas cichlid species formed in sympatry show divergent allometric trajectories and species diverge at entire modules of co-expressing genes
• In addition to diverging in a number of morphological traits, at least one Midas cichlid species pair formed in sympatry also shows divergence in gut microbiota
• Midas cichlids and closely related species which do not speciate in sympatry have colonized at the same time the crater lakes where Midas cichlids speciate. Therefore, some other reason makes Midas cichlids “special” and able to speciate in sympatry

Several more can be found either in the Publications page or in my Google Scholar profile. Also, further studies on this topic are under way.

*=shared first-authorship

• Franchini, P.*, Fruciano, C.*, Spreitzer, M.L., Jones, J.C., Elmer, K.R., Henning, F., Meyer, A. 2014. Genomic architecture of ecologically divergent body shape in a pair of sympatric crater lake cichlid fishes. Molecular Ecology 23(7): 1828-1845.
• Fruciano, C.*, Franchini, P.*, Kovacova, V., Elmer, K., Henning, F., Meyer, A. 2016. Genetic linkage of adaptive traits in sympatrically speciating Midas cichlid fish. Nature Communications 7: 12736.
• Fruciano, C., Franchini, P., Raffini, F., Fan, S., Meyer, A. 2016. Are sympatrically speciating Midas cichlid fish special? Patterns of morphological and genetic variation in the closely related species Archocentrus centrarchus. Ecology and Evolution 6(12):4102-4114.
• Fruciano, C., Meyer, A., Franchini, P. 2019. Divergent allometric trajectories in gene expression and coexpression produce species differences in sympatrically speciating Midas cichlid fish. Genome Biology and Evolution 11(6): 1644–1657.