Original paper

Are hybridization and polyploidization phenomena detectable in the fossil record? A case study on otoliths of a natural hybrid, Poecilia formosa (Teleostei: Poeciliidae)

Schulz-Mirbach, Tanja; Scherb, Hagen; Reichenbacher, Bettina

Abstract

Hybridization and polyploidization phenomena play an important role for speciation processes. In the fossil record, however, evidences of such phenomena are difficult to identify. We studied whether effects of hybridization and polyploidization are visible in the morphology of fish otoliths. Otoliths are massive calcium carbonate concretions positioned in the inner ear of teleost fishes. Thus, otoliths possess a high preservation potential and often provide the sole fossil remains of teleost fishes since Cretaceous times. As an extant model, we chose the natural hybrid Poecilia formosa and the parental species P. latipinna and P. mexicana. We analyzed otolith contours (N = 170) using Fourier shape analysis. In addition, the height to length ratio was calculated. Otoliths of P. formosa were found to be clearly distinct from P. latipinna and P. mexicana, and their otolith contours were intermediate to those of the two parental species. However, otolith contours of P. formosa were slightly more similar to those of P. mexicana, which represents the "maternal part" of the hybridization event. In part, the otolith contour and the height to length ratio revealed distinct differences between populations (two diploid, one triploid population) of P. formosa. We suggest that these differences may be a result of geographic differentiation and to a minor degree due to differences at the ploidy level. Our study shows that it may be possible to trace hybridization in the fossil fish record based on otolith morphology.

Keywords

poeciliidaeotolithhybrid speciestriploidgeographic differentiationshape analysismorphometry