Genetic relationships of the colour morphs of Acanthochromis polyacanthus (Pomacentridae) on the northern Great Barrier Reef |
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Authors: | S Planes P J Doherty |
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Institution: | (1) Australian Institute of Marine Science, PMB 3, Townsville, Queensland 4810, Australia, AU |
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Abstract: | Acanthochromis polyacanthus is an unusual tropical damselfish because it lacks pelagic larvae and has lost the capacity for broad-scale dispersal among
coral reefs. On the modern Great Barrier Reef, this fish has multiple colour morphs and we have previously described steep
genetic clines in the central region between three colour morphs. A similar transition of colour morphs has been found in
the far northern region (Latitude 11°S), where at least five colour morphs and intergrading hybrids were found during a survey
of 14 locations on nine adjacent reefs. On two of these reefs, monochromatic white and bicoloured morphs coexist, partitioning
the reef slope vertically when sympatric, but occupying the full depth range elsewhere. In areas of overlap, they interbreed,
producing hybrids of intermediate colour. Although the discriminatory power of our genetic analysis was weakened by the low
level of variability in these populations (only four polymorphic loci), allozyme electrophoresis revealed significant genetic
differentiation within and among reefs. There was neither simple linkage between colour and protein variation, nor correlation
between genetic similarity and proximity of sampled populations. We suggest that the observed chaotic structure is the result
of differences among the founding populations, although the two colour-based stocks have been homogenized through a long history
of introgression during multiple episodes of isolation and secondary contact. Despite genetic mixing, phenotypic diversity
(i.e. colour morphs) seems to have been preserved in these populations by sexual selection, perhaps reinforced by natural
selection. The long-term stability of this outcome, however, is suggested by the presence of unique morphs on two reefs that
are detached from the continental shelf and surrounded by very deep water. The strong identity of these populations can be
attributed to long occupation of these isolated sites compared with those on the continental shelf which have only been established
in the last 15 000 yr and still retain differences arising from the initial founder events.
Received: 15 January 1997 / Accepted: 15 August 1997 |
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