An examination of introgression and incomplete lineage sorting among three closely related species of chocolate‐dipped damselfish (genus: Chromis)

Abstract

Aim To determine the impact of ecological and environmental histories on the evolution of coral reef damselfishes at two adjacent marine biogeographic suture zones. Location Indo‐West Pacific, notably including two suture zones: Socotra and Christmas and Cocos/Keeling Islands. Taxon Chromis dimidiata , Chromis margaritifer , and Chromis fieldi . Methods We utilized a combination of nuclear and mitochondrial genetic markers in addition to visual abundance survey data of these fishes. Results Despite genetic patterns consistent with incomplete lineage sorting and relatively low genetic differentiation among the three studied Chromis species, there is evidence of hybridization between C. margaritifer and C. fieldi at Christmas Island based on molecular and visual identification. Introgression appears to be spreading westwards to other C. fieldi populations based on COI haplotype comparison. Moreover, the genetic distance between C. margaritifer and C. fieldi suggests that Pleistocene sea‐level fluctuations may have contributed to allopatric divergence and secondary contact between these two closely related species. Main conclusions Our study highlights that evolutionary processes in coral reef fishes operate differently between suture zones, possibly due to different ecological and environmental predispositions regulating secondary contact of sister species. While secondary contact likely led to hybridization and introgression at Christmas and Cocos/Keeling Islands, none of those processes seem present at Socotra for the chocolate‐dipped damselfish. This difference is likely due to an environmental barrier caused by hydrodynamic regimes in the Gulf of Aden.

Systematics of Damselfishes

“…He specifically commented on its XIII dorsal spines and lack of filamentous caudal rays. Even though the bicolor species with abrupt dark-tolight color patterns do not form a monophyletic group within Pycnochromis, a subset of them (P. abruptus, P. dimidiatus, P. fieldi, and P. margaritifer) are closely related (100% bootstrap), which has been proposed before (Randall, 2001;Allen and Erdmann, 2012;Randall and DiBattista, 2013;He et al, 2019b). Our results corroborate the sister relationship hypothesized for P. abruptus (¼ Chromis sp.…”

Distinct patterns of hybridization across a suture zone in a coral reef fish (Dascyllus trimaculatus)

“…Until recently, hybridization was considered relatively rare in marine environments (Arnold, ). However, ongoing ecological and molecular research in marine suture zones has led to a stark increase in the number of confirmed cases of hybridization (DiBattista et al, ; He et al, ; Hobbs & Allen, ; Hobbs, van Herwerden, Pratchett, & Allen, ; Montanari, Hobbs, Pratchett, & van Herwerden, ). To date, two major marine suture zones have been recognized for coral reef fishes: the well‐studied zone that encompasses Christmas Island (CHR) and Cocos (Keeling) Islands (CKE) in the eastern Indian Ocean (Hobbs & Allen, ; Hobbs, Frisch, Allen, & Van Herwerden, ), and the less explored zone in the Socotra Archipelago (DiBattista et al, ).…”

“…Previous studies suggest a potential bias when reporting these instances, as most cases belong to sister species that produce hybrids with a clear intermediate coloration, such as butterflyfishes (Chaetodontidae; Hobbs & Allen, ). Further, 14 out of those 15 hybrid cases are from broadcast spawning species, the other case is for substrate spawners Chromis fieldi and C. margaritifer (He et al, ). Damselfishes (family Pomacentridae) are one of the most diverse families of coral reef fishes, and hybridization events are not uncommon (i.e., anemonefishes, Litsios & Salamin, ).…”

Species delineation and hybrid identification using diagnostic nuclear markers for Mediterranean groupers Epinephelus marginatus and Mycteroperca rubra

“…Several approaches have been utilized for hybrid detection. According to previous studies, intermediate coloration (Kemp, 2000;Marie et al, 2007;Hobbs et al, 2013;Hobbs and Allen, 2014;DiBattista et al, 2015), morphology comparison (Wang et al, 2014;He et al, 2019a;He et al, 2020), isozyme electrophoretic patterns (Sick et al, 1963;He and Mork, 2015), diagnostic nuclear marker (van der Meer et al, 2012;Bernardi et al, 2013;Walter et al, 2014;Qu et al, 2018;He et al, 2018a;He et al, 2019b), microsatellites (Harrison et al, 2014;He et al, 2019a;He et al, 2019b;He et al, 2019c), and even genome-wide sequence comparison (Montanari et al, 2014) are all good candidates for identifying and confirming hybridization cases. Diagnostic nuclear markers are one of the most cost-efficient and robust methods with relatively high accuracy for hybridization detection purposes (He et al, 2018a).…”