Dissertation - HQ

General questions on behavioural traits 29
of information available on any particular behaviour is limited to relatively
few species, and to only a portion of the larval stage (usually
older larvae). When deciding if behavioural information from species A
can justifiably be used in a model for species B, two things must be
considered at the outset: the evolutionary closeness of the two species
and the similarity of the environment in which the species live.
The vast diversity of teleost fish species — approximately 27000
species in 448 families divided among 40 Orders 66 — means that some
species are very distantly related, with evolutionary histories that have
been separate for tens of millions of years. Particularly among Orders,
there is no reason to assume that behaviours will be similar. Within
mammals, for example, no one would assume that the behaviour of
a Tiger (Order Carnivora) would be similar to that of Dugong (Order
Sirenia), just as no one should assume that the behaviour of a Plaice
larva (Order Pleuronectiformes) would be similar to that of a Herring
larva (Order Clupeiformes). As a general rule, in the absence of other
information, the closer two species are related, the more justifiable
it should be to assume they have equivalent behaviour. The use of
well-corroborated phylogenies that encompass the species under consideration
is essential in assessing the closeness of relationships, but
for many fish taxa such phylogenies do not exist. Even this general
rule should be applied cautiously, because there are many examples of
larvae of confamilials with different behaviours. For example, larvae
of some pomacentrid species are found in midwater, whereas those
of other species prefer the top few centimetres of the water column 67 .
At this point in our knowledge of the behaviour of fish larvae, it is
difficult to make any defendable statement about how closely related
two species must be before it is justified to assume the behaviour of
their larvae is similar. An analysis of behaviour of fish larvae in the
context of phylogeny to help establish if relatedness provides a sound
basis for inferring behaviour would be most useful.
It is unlikely that, even within a family, the larvae of a species that is
pelagic as an adult will behave similarly to the larvae of a species that
lives on a coral reef, or in an estuary. Therefore, if it is not possible to
obtain behavioural data on the species of interest, the species supplying
the behavioural data should at least live in the same habitat as the
species of interest, both in the adult and larval stages. Echoing the
comment above, an analysis of behaviour of fish larvae to determine
to what extent habitat similarity provides a sound basis for inferring
behaviour would be very valuable.
Overall, the use of behavioural data from a distantly related species
that lives in a different habitat should be avoided at all cost. Finally,
there are indications that swimming speed can be predicted from the
morphology of the larvae 68 . Therefore, the use of swimming data from
species with similar larval morphology might be appropriate.
Cross-Order
generalisations
do not make sense
Adult lifestyle influences
larval behaviour