2. a) Compare and contrast genetic determination
and condition-dependent determination of as proximate causes of
alternative male strategies. b) Give a biological example of
each kind of determination.
10 points to accurately compare and contrast the two types of determination
10 points to give a biological example of each (to get full credit must descripe morph types and their strategies)
Many alternative male types are thought to be condition-dependent
strategies in which an organism's internal physiological (e.g.,
nutrition, age, or body size) interacts with environmental factors
(e.g., food availability, hatching date, etc) to alter development
of morphology and behavioral. Differences in morphology and behavior
are not governed by genetic factors such as alternative alleles.
Blue-gill sunfish have three alternative male phenotypes, however,
the attempt to isolate alternative alleles that control such behaviors
have not been successful. It is thought that when males mature
into three different-sized male types with different behaviors,
the trigger for the three states, is the overall body-size at
maturation. Males in good condition may mature later, and grow
into a large territorial male, that defends a small area in which
females deposit their eggs, medium sized males are female mimics,
and small males sperm bomb.
Under genetic models of sex determination male morphology and
behavior is explicitly controlled by a single gene with alternative
alleles or perhaps several genes. The environment plays very little
role in determining the phenotype. The data on ruff pedigrees
can descriminate between between several simple mendelian patterns
of inheritance. Their pedigree data is consistent with an autosomal
gene with Satellite dominant. (The other morph is the dominant
that gets the center part of the lek) While the previous example
of male ruffed grouse provides solid evidence of major genes which
affect the phenotype, the sample size in these studies is still
inadequate to test for the existence of other genetic loci that
control development of male behaviors.
OR
The final example of genes with major effect involves the genetic control of alternative male behaviors in a marine isopod
1.a large alpha male with elongate posterior appendages that they use to defend harems of
females
2.a medium-sized beta male that can invade female harems by mimicking female behavior
and morphology, and
3.a small-sized gamma male that invades female harems by virtue of its secretive
behaviors.
Shuster has developed a genetic model that explains patterns of inheritance of the three morphs. Three alleles at the Alternative male strategy (Ams) locus provide a reasonable explaination of the general pattern of inheritance of the male morph.