The influence of self-fertilization and grouping on fitness attributes in the freshwater snail Physa acuta: population and individual inbreeding depression
P. Jarne et al., The influence of self-fertilization and grouping on fitness attributes in the freshwater snail Physa acuta: population and individual inbreeding depression, J EVOL BIOL, 13(4), 2000, pp. 645-655
The genetic structure, selfing rate and inbreeding depression of the hermap
hroditic freshwater snail Physa acuta were jointly analysed in a population
near Montpellier, France. Allozymic markers revealed moderate gene diversi
ty (0.138), and no heterozygote deficiency. The mean outcrossing rate, esti
mated by using progeny arrays, was 0.9, with substantial variation among fa
milies. This also suggests that the number of fathers among outcrossed offs
pring of a given mother is low. Inbreeding depression was estimated over mo
re than one generation using 83 first-laboratory-generation (G(1)) families
. The main parameters measured were parental (G(1)) fecundity, offspring (G
(2)) survival and fecundity. Size and growth were also monitored. Parental
fecundity was analysed under several conditions (isolation, pair and quadru
plet outcrossing). The self-fertilization depression, including parental fe
cundity, offspring survival and fecundity, was about 0.9 at the population
level. The genetic data obtained in the same population indicate a value of
about 0.3 using Ritland's (1990) technique, suggesting that the depression
over the whole life-cyle might be even higher than 0.9. Grouping affected
neither fecundity nor self-fertilization depression. Substantial variation
in depression for survival was detected among individuals, from no survival
in some selfed families to better survival than that of outbred families i
n others. The overall result (outbred population structure, high outcrossin
g rate and high self-fertilization depression) is consistent with what is e
xpected in large outcrossing populations in which inbreeding depression is
maintained by mutation-selection balance.