Question

Based on what you have learned about inclusive
fitness theory in eusocial insect colonies,
you might assume that D. discoideum slugs
always consist of relatives and that the nonreproducing
stalk cells would be favored by kin
selection. But what if we told you that more than
half of the slugs studied in the lab contained
chimeric mixtures of multiple amoeba strains
(Strassman et al. 2000)?
Joan Strassman and David Queller have
argued that these chimeric slugs set the stage
for social conflict (see later in this chapter)
and the evolution of freeloading or cheater
behavioral strategies. In other words, because
slugs are potentially a mixture of unrelated
amoeba strains, some strains may cheat and
form fruiting bodies, but not stalks, giving them
a better chance at passing along their genes
to the next generation. Given these concerns,
could you still use kin selection theory to make
a prediction about the genetic similarity of the
strains that work together? Why or why
not? You might wonder, for example, if
D. discoideum in the lab form chimeras because
they come into contact with other strains in
ways that they might not in nature. It turns out
that researchers led by Strassman and Queller
have found that chimeras also form in nature
(Fortunato et al. 2003). For kin selection to
work, relatedness among cells must be high.
What would the average relatedness among
cells be in this asexually reproducing species
if all of the amoebae were of a single strain? It
turns out that the average relatedness of cells in
wild-caught slugs is 0.52 (Fortunato et al. 2003),
or equivalent to that of parents and offspring,
or of siblings, in diploid species. However,
follow-up studies using additional fruiting bodies
from various locations and times of year found
slightly higher relatedness values of 0.68 in
chimera fruiting bodies and values of 0.98 in
non-chimeric fruiting bodies (Gilbert et al. 2007).
Given these results, what can you conclude
about the role that kin selection plays in the lives
of social amoebae?

Answer 1

If more than half of the slugs used in laboratory are chimeric mixtures,then possiblity is if D.discoideum species have amoebae with different mating genes or they may interact with other unrelated species when the environmental conditions are suitable for their mating. For eg: Hetrothallic mating of D.discoideum occurs when two amoebae of different mating genes are present in dark and wet environment,this leads to formation of zygote during aggregation.In such case, it will lead to production of fruiting bodies by sexual reproduction rather than favouring non-reproducing stalk cells as mentioned in kin selection.In such case kin selection theory may become less reliable.