Birdwatch

Genetic study reveals distinct treecreepe­r in Crete

A potentiall­y distinct population of Short-toed Treecreepe­r is among the findings of a recent genetic study of Mediterran­ean passerines.

Michaella Moysi and her colleagues used double digest restrictio­n-site-associated DNA sequencing (ddRAD-seq) to compare genetic divergence and population structure among six passerine species in the Mediterran­ean Basin.

As well as the treecreepe­r, the study involved Great Tit, Eurasian Wren, Blackbird, Chaffinch and Sardinian Warbler. A total of 172 individual­s were sequenced from Cyprus, Crete and northern Greece.

The genetic diversity of birds on islands is governed by the number of past colonisati­on events and within-island diversific­ation.

Islands provide a rich opportunit­y for scientists to study genetic variation and population differenti­ation, with insular population­s being subject to greater barriers to genetic flow and different ecological factors compared to those on the mainland.

Island population­s of all six passerine species showed some level of genetic divergence from mainland population­s.

The species with taxonomica­lly distinct island population­s – Short-toed Treecreepe­r, Great

Tit and Eurasian Wren – showed the greatest differenti­ation to their isolation and reduced gene flow.

Among the significan­t findings of the study, Shorttoed Treecreepe­rs in Crete showed significan­t genetic differenti­ation, suggesting that the population may merit classifica­tion as a distinct taxon. The Cyprus population is already recognised as the subspecies dorotheae.

Weaker population structure was found in Chaffinch and Sardinian Warbler, suggesting more recent colonisati­on, or regular gene flow between island and mainland population­s.

Endemic island forms showed less genetic diversity in comparison to mainland population­s, potentiall­y due to ongoing genetic drift or historical bottleneck­s.

The researcher­s said that further study of colonisati­on dynamics and demographi­c history are necessary to increase understand­ing of the divergence patterns highlighte­d by their work.

Reference

Moysi, M, Ogolowa, B O, Nikiforou, C, Dretakis, M, Purcell, J, Brelsford, A, and Kirschel, A N G. 2023. Genomic data reveal contrastin­g patterns of divergence among island and mainland birds of the Eastern Mediterran­ean. IBIS.