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A stable, genetically determined colour dimorphism in the dung beetle A phodius depressus : patterns and mechanisms
Author(s) -
KUUSIJÄRVI ANNIINA,
HARDWICK BESS,
LUOTO MISKA,
ROSLIN TOMAS
Publication year - 2015
Publication title -
ecological entomology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.865
H-Index - 81
eISSN - 1365-2311
pISSN - 0307-6946
DOI - 10.1111/een.12223
Subject(s) - biology , melanism , cline (biology) , sexual dimorphism , zoology , thermoregulation , ecology , aposematism , evolutionary biology , predation , predator , population , demography , sociology
1. Melanism – the occurrence of dark morphs – in insects has been attributed to differences in, among other things , thermoregulation and immune defence. Dark individuals are hypothesised to perform better in colder areas, and to exhibit stronger melanin‐based immune defence. 2. In the present study, the geographical distribution of two colour morphs in A phodius depressus ( K ugelann), its climatic correlates, and temporal stability was described. Underlying mechanisms were then targeted through experiments: the inheritance of colour through controlled crosses, heating rates by thermal imaging, physiological tolerance by critical thermal limits, and immune efficiency by melanisation of implants. 3. In A. depressus , colour appears inherited by simple M endelian principles, with red dominating over black. The frequency of two colour morphs forms a large‐scale cline. In the S outh W est of F inland, all individuals are black, whereas, in the N orth E ast, most are red. This pattern has remained constant over 13 years (1996–2008). 4. The geographical pattern was not attributable to thermoregulation: black morphs were more abundant in warmer rather than colder parts of the country. In experiments, we found no differences in the heating rate of the two morphs, or in their upper temperature maxima. Neither did the morphs differ in their response to artificial objects inserted in their haemolymph. 5. Overall, colour variation in A. depressus occurs as a stable, genetically determined dimorphism, governed by M endelian inheritance. Yet, no support for prevailing theory of factors sustaining melanism was found. The reasons for colour polymorphism in insects may thus be complex, and should be sought on a case‐by‐case basis.