Cocos Keeling?

[Giovanni]

What is so special about fish and other animal from Cocos Keeling?

 

[Dmorty217]

They have a better coloration than their counterparts. Ie the lemonpeel from Cocos has better blue coloring around the eye. The Joculator comes from there, so that makes it pretty cool

 

[ThRoewer]

The Cocos/Keeling Islands and Christmas Island are on the biogeographic border between the eastern Indian and Pacific Ocean's regional biotas. There is a good deal of overlap which favors hybridization that may lead to new species. Also, both locations are somewhat isolated which favors endemism.


Here two articles about that region:
Hybridization of reef Wshes at the Indo-Pacific biogeographic barrier: a case study (full article)

Abstract
Hybridization is recognized as an important source of genetic variation. In some reef fishes, including the Acanthuridae, hybridization has been detected due to intermediate colouration. This study used a molecular genetic approach to investigate hybridization in two Acanthurid species: Acanthurus leucosternon and Acanthurus nigricans, which have Indian and Pacific Ocean distributions respectively and are sympatric in the eastern Indian Ocean. In this area a putatitve hybrid, Acanthurus cf. leucosternon has been recognized based on intermediate colouration and restriction to the sympatric region of otherwise allopatric putative parental species. This study aimed to test this hypothesis using genetic tools. The three species were sampled from Cocos (Keeling) and Christmas Islands, the biogeographic boundary where many Indian and Pacific Ocean biota meet. Representatives from allopatric populations of both parental species and outgroups were also sampled. Mitochondrial COI and intron 1 of the nuclear ribosomal protein S7 were sequenced from 13 and 30 specimens respectively. Although sample sizes in this study are relatively small and more genetic data, including an extended phylogeographic sampling, is required to further evaluate these Wndings, the COI results support hybrid origins of Acanthurus cf. leucosternon, but S7 data are inconclusive due to the possibility of incomplete lineage sorting. The fourfold more abundant Acanthurus nigricans is most often the maternal parent. Inter-fertile hybrids apparently backcross with rare Acanthurus leucosternon males, transferring Acanthurus nigricans mitochondria to this species. These results suggest that Acanthurus leucosternon may eventually be lost from these islands, due to their relative rarity and introgressive hybridization.

Marine hybrid hotspot at Indo-Pacific biogeographic border (full article)

Abstract

Studying hybridization is crucial to understanding speciation and almost all our knowledge comes from terrestrial and freshwater environments. Marine hybrids are considered rare, particularly on species-rich coral reefs. Here, we report a significant marine hybrid zone at Christmas and Cocos Islands (eastern Indian Ocean) with 11 hybrid coral reef fishes (across six families); the most recorded hybrids of any marine location. In most cases, at least one of the parent species is rare (less than three individuals per 3000 m2), suggesting that hybridization has occurred because individuals of the rare species have mated with another species owing to a scarcity of conspecific partners. These islands also represent a marine suture zone where many of the hybrids have arisen through interbreeding between Indian and Pacific Ocean species. For these species, it appears that past climate changes allowed species to diverge in allopatry, while recent conditions have facilitated contact and subsequent hybridization at this Indo-Pacific biogeographic border. The discovery of the Christmas–Cocos hybrid zone refutes the notion that hybridization is lacking on coral reefs and provides a natural laboratory for testing the generality of terrestrially derived hybridization theory in the marine environment.



Figure 1 (click to enlarge)
Christmas and Cocos Islands (represented by five-pointed stars) constitute a tropical marine suture zone located in the eastern Indian Ocean on the Indo-Pacific marine biogeographic border. At these islands, Indian (represented by lighter shaded area with dashed outline) and Pacific Ocean species (darker shaded area with solid outline) have come into contact and interbred.



Figure 2 (click to enlarge)
Christmas and Cocos Islands constitute a marine suture zone where (a) Indian Ocean (C. eibli) and (b) Pacific Ocean species (C. flavissima) come into contact and interbreed to produce (c) hybrids. (d) Heterospecific breeding pairs of Ch. guttatissimus (Indian Ocean: bottom) and Ch. punctatofasciatus (Pacific Ocean: top) produce (e) hybrids. (f) Heterospecific breeding pair of Indian (Ch. trifasciatus: bottom) and Pacific Ocean (Ch. lunulatus: top) butterflyfishes.

 

[ThRoewer]

A pretty long list of fish you find at Christmas Island:

FISHES OF CHRISTMAS ISLAND, INDIAN OCEAN
Gerald R. AlIen