Zusammenfassung
Variation in paternity frequency in colonies of eusocial
insects has profound effects on the relatedness among offspring and on
the genetic diversity of colonies. Data on queen 'mating-frequency'
in eusocial Hymenoptera vary in both quality and the phase of the
'mating' process they address. Some are observational studies of
the range or maximum number of copulations; others are derived from
estimates of the number of sperm in males and queens; others use genetic
techniques to determine the paternity of different males among female
offspring. Only the latter data can be used to calculate relatedness among
offspring females. Previous reviews drew attention to these problems, but
their results have established the impression that high paternity
frequencies are common, largely because multiple copulations are
frequently observed. For ants, we show that: (i) the range of observed
copulations overestimates effective paternity frequency; and (ii) the
mean effective paternity frequency in 19 species, for which accurate
data based on allozyme analysis of mother - offspring combinations
are available, is only 1.16 (range 1-1.48). Over one third of these
species have queens in which only one male contributes to paternity.
Data from 34 species, which include less detailed genetic studies
and four species studied using sperm counts, give similar results.
Only two species, both Atta leaf cutter ants and both studied using
data on sperm stored in queen spermathecas, appear to have effective
insemination frequencies above two. Data on bees and wasps show a
similar trend, We conclude that reliably documented high paternity
or insemination frequencies (> 2) are currently restricted to one
phylogenetically isolated and highly eusocial taxon each in ants, eusocial
bees and wasps (Atta, Apis and Vespula, respectively). This pattern
justifies the working hypothesis that multiple mating, by lowering the
relatedness between female offspring and thereby the benefits of
reproductive helping behaviour, has not been a general constraint for
the evolution of eusociality in the Hymenoptera.Using reliable data
on paternity frequency and insemination, we re-analyse two factors
that it has been suggested correlate with mating frequency: colony
population and number of egg-laying queens per colony. We find the
following.1. There is a significant positive correlation between
paternity/insemination frequency and colony size for monogynous ants, but
not for polygynous ants. This result seems to support the 'sperm
limitation' hypothesis, that queens which need to be highly fecund
copulate multiply to store sufficient sperm. We note, however, that
the same trend is expected when large and/or long-lived colonies
profit more from having genetically diverse offspring.2. There is
no significant negative correlation between paternity/insemination
frequency and number of queens per colony. However, when the analysis is
restricted to species with large colonies and no intranidal mating, the
correlation between paternity frequency and queen number becomes marginally
significant. Several previous reviews have addressed the possible adaptive
significance of multiple paternity. In contrast, and in keeping with the
data that show single paternity to be frequent, we discuss selective
reasons for single or low paternity. We compare the relative effects of
multiple paternity and multiple maternity on genetic diversity within
colonies and show that they are not equivalent, and we also discuss
directions for future research on paternity issues in social insects.
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