Ecology and life history evolution among freshwater invertebrates,
particularly among the Unionoida (Naiads)
Important correlations among naiad life history traits are a) a
negative relationship between metabolism and life span, b) a trade
off between glochidial size and fertility and c) a positive relationship
between glochidial size and size of the host range.
The freshwater pearl mussel (Margaritifera margaritifera) lives
in headwater streams poor in nutrients. The reduced metabolism,
(an adaptation to the low food supply), combined with low summer
temperatures, leads to a very long life of more than 100 years.
The prevalence of Salmonids in these rivers makes a narrow host
range possible and thus a reduction of glochidial size, leading
to an increase in fertility. This strategy leads to a high life
time fertility through a high number of reproductive periods and
a high number of glochidia per reproductive period.
On the other hand, two Anodonta species live in large rivers or
standing waters of high trophic level. They are "a priori"
short lived due to high summer temperatures, and they cooccur with
a diverse fish fauna. Their strategy maximizes the size of the host
range, (i.e. the number of fish species where glochidia can develop).
This reqires large glochidia, which are kept for many months in
highly developed marsupia. The low fertility is compensated for
by a behavioral adaptation to increase glochidial survival. They
perceive the presence of host fish and then release some glochidia.
Unio crassus, which prefers intermediate river sections, also occupies
an intermediate position with respect to life span, size of the
host range, glochidial size and fertility. Due to the small body
size, fertility is low, which is compensated for by producing some
consecutive broods per reproductive season.
The growth process, i.e. life span, growth rate, body size, shows
a great deal of phenotypic plasticity. On the other hand, traits
closely related to the host relationship, i.e. glochidial size and
host range, seem to be canalized.
Interactions between the reproductive strategy of plants and
Rhagoletis alternata is a common tephritid fly in Central Europe,
whose larvae feed on the hypanthium of rose hips. The resource -
consumer system is "non-interactive", i.e. the insect
has little or no impact on its host plant's fitness and therefore
is not able to influence the rate at which larval food resources
The exploitation strategy of this insect has been investigated and
shall be compared to an interactive system, namely the beech and
its seed predator Cydia fagiglandana (Lep. Tortricidae).