Integrative taxonomy of the sea star Astropecten irregularis (Pennant, 1777) species complex in the North Sea.
Supervisor: Pedro Mtnez Arbizu (German C. Mar Biod Res)
The sea star genus Astropecten Gray, 1840 includes 104 valid species and has a complex taxonomic history as new species, subspecies, and varieties have been described based on highly-variable external morphological characters. This is the case of Astropecten irregularis (Pennant, 1777) and particularly, two distinct lineages were previously detected by DNA barcoding in the North Sea. The present work aims to determine the specific boundaries of the A. irregularis species complex in the North Sea by morphological comparisons between the two lineages and museum material, exploring their genetic variability through DNA barcoding and 2b-RAD (Restriction Site-Associated) sequencing so complete lineage sorting across the whole genome can be compared, and using MALDI-TOF (Matrix Assisted Laser Desorption Ionization Time-Of-Flight Mass Spectrometry) as an identification method based on specific proteome fingerprints. No differences based on external morphology were found, highlighting the high variation in both inferomarginal and subambulacral spination. Likewise, the lack of A. irregularis type material and clear differences between Astropecten acicularis Norman, 1865 and A. irregularis irregularis museum material did not allow for accurate morphological identification for the two lineages of A. irregularis irregularis; thus, here they were considered as A. cf. irregularis irregularis 1 and A. cf. irregularis irregularis 2. Both DNA barcoding and MALDI-TOF provided congruent identifications of unknown specimens (with the exception of the specimen DANA 592.5), showing its reliability to detect the two well-supported, distinct lineages of A. irregularis irregularis. 2b-RAD sequencing also supported the separation A. cf. irregularis irregularis 1 and A. cf. irregularis irregularis 2 as different cryptic species. A. cf. irregularis irregularis 1 has a northern distribution, and a bathymetric range from 72.6-160.1 m; with the exception of 00 specimen found at 24 m. With respect to A. cf. irregularis irregularis 2, it has a southern distribution, with a bathymetric range from 18 to 141.6 m; except for DANA 252.4 and DANA 252.5, specimens found at 152.7 m. Likewise, both lineages were reported at five stations. As no hybrids were detected, the existence of potential hybrid zone at a certain intermediate depth should be explored using 2b-RADs data from additional individuals. This is the first integrative taxonomic study combining the above methods to gain further insights into the genetic differences of cryptic species, as well as both bathymetric and geographical distribution of Astropecten species.

Keywords: cryptic species, DNA barcoding, 2b-RAD, MALDI-TOF, morphology.