The Genetics of Behavior
The Genetics of Behavior
The hereditary transmission of most innate behavior is complex, with many interacting genes regulating each behavioral trait. However, there are a few examples of behavioral differences within species that show simple Mendelian transmission from parents to offspring. Perhaps the most convincing example is the inheritance of hygienic behavior in bees. Honey bees are susceptible to a bacterial disease, American foulbrood (Bacillus larvae). A bee larva that catches foulbrood dies. If the bees remove dead larvae from the hive they reduce the chance of the infection spreading.
Some strains of bees, called “hygienic,” uncap hive cells containing rotting larvae and carry them out of the hive. W. C. Rothenbuhler found that there are two components to this behavior: first removal of cell caps, and second removal of larvae. Hygienic bees have homozygous recessive genotypes for two different genes. Uncapping behavior is performed by individuals homozygous for a recessive allele, u, at one gene, and removal behavior is performed by individuals homozygous for a recessive allele, r, at a second gene. When Rothenbuhler crossed hygienic bees (u/u r/r) with a nonhygienic strain (U/U R/R), he found that all the hybrids (U/u R/r) were nonhygienic. Thus only workers having both genes in the homozygous recessive condition show the complete behavior. Next, Rothenbuhler performed a “backcross” between the hybrids and the hygienic parental strain. As we should expect if hygienic behavior is transmitted by allelic variation of two genes, four different kinds of bees resulted (Figure 38-5). Approximately one-quarter of the bees were homozygous recessive for both u and r and showed the complete behavior: they both uncapped the cells and removed the bees. Another quarter of the offspring (u/u R/r or u/u R/R) uncapped but did not remove dead bees. Another quarter (U/u r/r or U/U r/r) did not uncap, but would remove the larvae if another worker uncapped the cells. Workers that were homozygous or heterozygous for the dominant allele at both genes (U/u R/r) would not perform either part of the cleaning behavior (Figure 38-5). The results showed clearly that each component of the cleaning behavior was associated with one, independently segregating gene.
Most inherited behaviors do not show simple segregation and independence; instead, hybrids of subspecies or species commonly show intermediate or confused behavior. A classic study of the effect of cross-breeding on behavior was carried out by W. C. Dilger on nest-building behavior in different species of lovebirds. Lovebirds are small parrots of the genus Agapornis (Figure 38-6). Each species has its own method of courtship and technique for carrying nesting material. Fischer’s lovebirds (A. personata fischeri) cut long strips of nesting material from vegetation, then carry this to the nest, one strip at a time. Peach-faced lovebirds (A. roseicollis) carry several strips of torn nesting material at one time by tucking them into feathers of the lower back and rump. Dilger, who was able to cross the two species successfully, found that hybrids displayed a confused conflict between a tendency to carry material in the feathers (inherited from the peach-faced lovebirds) and a tendency to carry material in the bill (inherited from Fischer’s lovebird) (see Figure 38-6). The hybrids attempted both feather-tucking and bill-carrying but performed neither behavior correctly. The hybrids had inherited a behavior that was intermediate between that of the parents. With experience hybrids improved their carrying ability by tending to carry the material in their bills, like Fischer’s lovebird.
The hereditary transmission of most innate behavior is complex, with many interacting genes regulating each behavioral trait. However, there are a few examples of behavioral differences within species that show simple Mendelian transmission from parents to offspring. Perhaps the most convincing example is the inheritance of hygienic behavior in bees. Honey bees are susceptible to a bacterial disease, American foulbrood (Bacillus larvae). A bee larva that catches foulbrood dies. If the bees remove dead larvae from the hive they reduce the chance of the infection spreading.
Some strains of bees, called “hygienic,” uncap hive cells containing rotting larvae and carry them out of the hive. W. C. Rothenbuhler found that there are two components to this behavior: first removal of cell caps, and second removal of larvae. Hygienic bees have homozygous recessive genotypes for two different genes. Uncapping behavior is performed by individuals homozygous for a recessive allele, u, at one gene, and removal behavior is performed by individuals homozygous for a recessive allele, r, at a second gene. When Rothenbuhler crossed hygienic bees (u/u r/r) with a nonhygienic strain (U/U R/R), he found that all the hybrids (U/u R/r) were nonhygienic. Thus only workers having both genes in the homozygous recessive condition show the complete behavior. Next, Rothenbuhler performed a “backcross” between the hybrids and the hygienic parental strain. As we should expect if hygienic behavior is transmitted by allelic variation of two genes, four different kinds of bees resulted (Figure 38-5). Approximately one-quarter of the bees were homozygous recessive for both u and r and showed the complete behavior: they both uncapped the cells and removed the bees. Another quarter of the offspring (u/u R/r or u/u R/R) uncapped but did not remove dead bees. Another quarter (U/u r/r or U/U r/r) did not uncap, but would remove the larvae if another worker uncapped the cells. Workers that were homozygous or heterozygous for the dominant allele at both genes (U/u R/r) would not perform either part of the cleaning behavior (Figure 38-5). The results showed clearly that each component of the cleaning behavior was associated with one, independently segregating gene.
 |
| Figure 38-5 The genetics of hygienic behavior in honey bees, as demonstrated by W. C. Rothenbuhler. The results are explained by assuming that there are two independently assorting genes, one associated with uncapping cells containing diseased larvae, and the other associated with removing the larvae from the cells. See text for further explanation |
Most inherited behaviors do not show simple segregation and independence; instead, hybrids of subspecies or species commonly show intermediate or confused behavior. A classic study of the effect of cross-breeding on behavior was carried out by W. C. Dilger on nest-building behavior in different species of lovebirds. Lovebirds are small parrots of the genus Agapornis (Figure 38-6). Each species has its own method of courtship and technique for carrying nesting material. Fischer’s lovebirds (A. personata fischeri) cut long strips of nesting material from vegetation, then carry this to the nest, one strip at a time. Peach-faced lovebirds (A. roseicollis) carry several strips of torn nesting material at one time by tucking them into feathers of the lower back and rump. Dilger, who was able to cross the two species successfully, found that hybrids displayed a confused conflict between a tendency to carry material in the feathers (inherited from the peach-faced lovebirds) and a tendency to carry material in the bill (inherited from Fischer’s lovebird) (see Figure 38-6). The hybrids attempted both feather-tucking and bill-carrying but performed neither behavior correctly. The hybrids had inherited a behavior that was intermediate between that of the parents. With experience hybrids improved their carrying ability by tending to carry the material in their bills, like Fischer’s lovebird.
 |
| Figure 38-6 Confused behavior in hybrid lovebirds (Agapornis sp.). The peach-faced lovebird carries nest-building
material tucked into its feathers; Fischer’s lovebird carries nest-building material in its beak. The hybrids attempted both carrying methods, neither method accomplished successfully. |
Support our developers
