Summary week 2 – Martine Maan
Developmental effects of visual environment on species-assortative
mating preferences in Lake Victoria cichlid fish
Bram Spierings | 950620790080 | Frontiers in Biology | 18-01-18
is the formation of distinct species within the course of evolution. Geographical
changes, barries (allopatric) or sexual selection (sympatric) are examples of
factors which are the driving process behind speciation. Previous studies
indicate that sympatric speciation could be driven by heterogeneous
environments when geographical obstacles are missing. An example of sympatric
speciation in a heterogeneous environment is the sensory speciation in two
species of Chichlids in Lake Victoria. Two closely related Chichlids, Pundamilia nyererei and Pundamilia pundamila live in the same
lake but differ in color and preference of waterdepth. P. pundamila lives in more shallow water habitat and the males are
grey/blue colored and P. nyererei lives
in more deeper waters and the males are yellow/red colored. Both species behave
as ‘real’ species when they are present in their prefered habitat but hybridize
in turbid habitat where.
State of the art
Although the aquatic ecosystem shows evidence in
visial communication, reproductive isolation due to visual adaptation hasn’t
been proved yet. Previous research to the effect of changing visual conditions
on mate choice for killifish did not show a comprehensive result but suggested
a small effect of sensory development on color choice. This promissing
suggestion is why the link between visual system properties and visual mate
preferences should be further investigated. Another study has found that p. nyererei expresses higher
long-wavelength-sensitive visual pigment and is more sensitive to red colors
compared to P. pundamila.
Furthermore, the characteristics of male coloration,
photic environment and female preferences are correlated with the visial
systems which the Chichlids prefer. However it is still uknown if these
adaptations are able to cause contrasting sexual color preferences. Therefore,
this study tries to answere if the visual development of both chichlids species
and their crossbreeds was manipulated to check its consequences for partner selection.
P. pundamila and P. nyererei
and their hybrids were reared in an experimental set-up in which different
light conditions simulated each prefered natural habitat. Visual development
was tested by checking female partner choice. Female preference was significantly affected by
the rearing light conditions.
pundamila was more in favor by
females which were reared in simulated shallow water habitat. The female chichlids
which were reared in deep water habitat did not have a specific preference for
any of the male chichlids species. The expression of retinal pigments might
influence female preferences. Higher expression of red sensitive pigment might
be caused by rearing in deep water and blue sensitive pigment in for females
which are being raised in shallow water.
Also, female chechlids do more
frequently respond to males of the same species when being reared in natural
lighting than when they are reared in artificial lighting. This could lead to
reproductive isolation because partner selection is formed by light conditions.
But as it turns out that the association between light circumstances and
partner preference is low it is unlikely that this is the only mechanism that
influences female preferences.
A second explanation for a certain
partner choice could lay in the fact that all fish were raised in family
groups. The females had contact with blue and red colored males before they
were tested. It might be possible that females are less likely to mate with a
certain colored male if they have never seen this color before.
An unexpected result, which was not
in line with a previous study, showed that females that were reared in natural
circumstances only weakly prefered males males with the same phenotype. An
explanation for this is that the previous experiment used aquarium lighting
instead of more natural lighting. A possible explanation for this is that there
was maternal imprinting did not took place. Earlier studies suggest that female
mate preference is affected by maternal imprinting which takes place in the
period when females care for their brood.
When juvenile fish are removed from their mother in this early lifestage
it might reduce the effect of imprinting. Another reason why female species
assortative preference is weak is the possible genetic simularity of the used
individuals. As the results indicate a low survival rate for in unnatural
conditions for both species it might also affect color prefence. The wild
caught mothers have certain characteristics that influence male choice and could
somehow have a higher rate of survival. If this is true it could lead to a
study group which is genetically simular and has no strong mate preference.
As last, not only sensory stimuli are affecting the
mating behaviour of chichlids. Mating behaviour between individuals also occurs
via chemical communication. A previous study indicates a higher activity and
succesrate of mating when chemical communication is possible compared to when
this was not. In this experiment female partner choice did not change when
chemical communication was possible. However, these tanks were larger than the
ones in which chemical communication was not possible and artifcial plants were in the tanks. Due to those difference it
is not possible to compare influence of chemical communication.
Discussion and conclusion
In general it can be stated that environmental conditions
influence both female chichlids species mate preferences. As expected, females reared in deep- and
shallow simulated habitats differ significantly in male preference and shallow
reared females prefer P. pundamila as mating partner. When females were
raised in circumstances that were not natural to their own species, a weaker
species-assortative preferences was noticed. This indicates that local habitat
heterogenity has effect on reproductive isolation and sympatric speciation. The
results claim that other factors influence female mate preference, but further
research is needed to understand this process.
Early life experiences possibly play an important role in
female preference. The coloration of males or maternal imprinting during this
life stage could affect female preference and could be studied by removing
juveline females from their mother and rearing them individually.
To better understand influence of light on female
prefences more information on the involved anatomical processes information on
genetic variation in visual systems and phenotypic plasticity is needed.