Biology Reference
In-Depth Information
Table 8.2
Distribution of male and female parental care with respect to mode of
fertilization in teleost fishes. The table shows number of families; a single family
may appear in more than one category, but is not listed under 'no parental care'
unless care is completely unknown in the family (Gross and Shine, 1981)
Internal fertilization
External fertilization
Male parental care
2
61
Female parental care
14
24
No parental care
5
100
female care is commonest with internal fertilization (86% female care) and male care
with external fertilization (70% male care). The overall predominance of male parental
care in fish is related to the prevalence of external fertilization.
Three hypotheses have been proposed to explain why mode of fertilization influences
which sex cares (Gross & Shine, 1981).
Uniparental male
or female care
common in fish
Hypothesis 1: Paternity certainty
Trivers (1972) suggested that reliability of paternity will be affected by mode of
fertilization. Since external fertilization occurs at the time of oviposition, reliability of
paternity may be greater than with internal fertilization where sperm competition may
take place inside the female's reproductive tract (Chapter 7). According to this
hypothesis, with internal fertilization a male should be less prepared to provide parental
care than the female because he is less certain that the offspring are his. While this idea
is sound in theory (Queller, 1997), it is not yet known whether paternity certainty really
is greater with external fertilization. In some external fertilizers, for example sunfish
Lepomis
, cuckoldry takes place during oviposition.
Three hypotheses
for why male care
is commonest
with external
fertilization and
female care with
internal
fertilization
Hypothesis 2: Order of gamete release
Dawkins and Carlisle (1976) suggested that, as with birds and mammals, internal
fertilization gives the male the chance to desert first and thus leave the female to care.
With external fertilization they suggested that the roles may be reversed; sperm are
lighter than eggs so perhaps the male must wait until the eggs are laid before he can
fertilize them, or else his gametes will float away. Therefore, the female has the
opportunity to desert first and swim off while the male is still fertilizing the eggs! This is
an ingenious idea but it must be rejected on empirical grounds. In fact, the most
common pattern of gamete release in external fertilizers is simultaneous release by
male and female. In these cases both sexes have an equal chance to desert, but 36 out of
46 species which have simultaneous gamete release and monoparental care have care
provided by the male. Secondly, in some families of fish (Callichythyidae, Belontiidae)
