A comparison of inbreeding depression in tropical and widespread Drosophila species

Abstract

The evolutionary history of widespread and specialized species is likely to cause a different genetic architecture of key ecological traits in the two species groups. This may affect how these two groups respond to inbreeding. Here we investigate inbreeding effects in traits related to performance in 5 widespread and 5 tropical restricted species of Drosophila with the aim of testing whether the two species groups suffered differently from inbreeding depression. The traits investigated were egg-to-adult viability, developmental time and resistance to heat, cold and desiccation. Our results showed that levels of inbreeding depression were species and trait specific and did not differ between the species groups for stress resistance traits. However, for the life history traits developmental time and egg-to adult viability, more inbreeding depression was observed in the tropical species. The results reported suggest that for life history traits tropical species of Drosophila will suffer more from inbreeding depression than widespread species in case of increases in the rate of inbreeding e.g. due to declines in population sizes.

Figure 1. Inbreeding depression for each of 6 traits (± SE) (a: ‘Developmental time’, b: ‘Egg-to-adult viability’, c: ‘Heat knock down resistance’, d: ‘Chill coma recovery time’, e: ‘Critical thermal minimum (CTmin)’, f: ‘Desiccation resistance’).

Data are split into 4 groups: tropical females (TF), tropical males (TM), widespread females (WF) and widespread males (WM). Horisontal lines represent averages for each of the 4 groups (TF, TM, WF, WM). The species are: D. bipectinata (bipect), D. birchii (birc), D. bunnanda (bunn), D. hydei (hydei), D. melanogaster (mel), D. pseudoananassae (ps), D. repleta (rep), D. serrata (ser), D. simulans (sim) and D. sulfurigaster (sulf). See ‘Materials and methods’ for a description of each assay.

Figure 2. Average inbreeding depression for the 10 species based on a) average inbreeding depression of the two investigated life history traits for each species (± SE) and b) average inbreeding depression of the four investigated stress resistance traits for each species (± SE).

Black bars are tropical species and grey bars are widespread species. Horizontal black lines represent averages for the tropical and widespread species. The species are: D. bipectinata (bipect), D. birchii (birc), D. bunnanda (bunn), D. hydei (hydei), D. melanogaster (mel), D. pseudoananassae (ps), D. repleta (rep), D. serrata (ser), D. simulans (sim) and D. sulfurigaster (sulf). Symbols: ‘T’ = ‘tropical’ and ‘W’ = ‘widespread’.