Keywords: Body color, camouflage, choice, damselfly, egg morphology, female polymorphism, oviposition, phenotypic integration, resource partitioning. Introduction Two or more coexisting species that utilize similar resources often demonstrate resource partitioning, and this partitioning has been hypothesized to reduce competition between the species Pyke ; Grant and Grant Materials and Methods Study species and study sites Ischnura senegalensis is a nonterritorial damselfly.
Open in a separate window. Figure 1. Observation of oviposition behavior In the two populations, oviposition behaviors were observed in and Statistical analyses Statistical analyses were performed using R version 2.
Results Morphological traits Average abdomen lengths in andromorphs Ozutsumi: Figure 2. Figure 3. Preference for oviposition resources Oviposition trials for the decaying tissue of Phragmites australis and Scirpus triangulates and the fresh living tissue of Typha spp.
Figure 4. Utilization efficiency Females very often altered oviposition location and laid eggs without competing for oviposition location with other females.
Figure 5. Discussion Disruptive selection induced by competition for limited resources is hypothesized to result in the evolution of resource partitioning Rueffler et al. Evolution of resource partitioning The female damselflies change oviposition localities very often to reduce the risk of predation on the eggs by aquatic predators and cannibalism among siblings when they hatch, and the total oviposition lasts 1—3 h in Ischnura Huang et al.
Genetic basis and maintenance of resource partitioning In this study, we observed a phenotypic correlation between body color, resource preference, and egg morphology. Ecological and evolutionary consequences The coexistence of multiple trophic morphs is predicted to result in some ecological and evolutionary consequences. Conflict of Interest None declared. References Abbott JK. Morph-specific and sex-specific temperature effects on morphology in the colour polymorphic damselfly Ischnura elegans.
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Resource polymorphisms in vertebrates. Linkage disequilibrium — understanding the evolutionary past and mapping the medical future. Evolutionary significance of resource polymorphisms in fishes, amphibians, and birds. A commonly discussed Punnett Square is the dihybrid cross.
A dihybrid cross tracks two traits. This means that both parents have recessive alleles, but exhibit the dominant phenotype. The phenotype ratio predicted for dihybrid cross is Of the sixteen possible allele combinations:. A simpler pattern arises when one of the parents is homozygous for all traits.
In this case, the alleles contributed by the heterozygous parent drives all of the variability. A two trait cross between a heterozygous and a homozygous individual generates four phenotypes, each of which are equally likely to occur.
More complicated patterns can be examined. In an extreme case when more than two alleles exists for each trait and the parents do not possess same alleles, the total number of genotypes equals the number of boxes in the Punnett Square.
It is possible to generate Punnett squares for more that two traits, but they are difficult to draw and interpret. A Punnett Square for a tetrahybrid cross contains boxes with 16 phenotypes and 81 genotypes.
A third allele for any one of the traits increases the number of genotypes from 81 to Given this complexity, Punnett Squares are not the best method for calculating genotype and phenotype ratios for crosses involving more than one trait.
Video Overview. Figure 2: In fruit flies, two possible body color phenotypes are brown and black. The substance that Mendel referred to as "elementen" is now known as the gene, and different alleles of a given gene are known to give rise to different traits.
For instance, breeding experiments with fruit flies have revealed that a single gene controls fly body color, and that a fruit fly can have either a brown body or a black body.
This coloration is a direct result of the body color alleles that a fly inherits from its parents Figure 2. In fruit flies, the gene for body color has two different alleles: the black allele and the brown allele.
Moreover, brown body color is the dominant phenotype, and black body color is the recessive phenotype. Figure 3: Different genotypes can produce the same phenotype. Researchers rely on a type of shorthand to represent the different alleles of a gene. In the case of the fruit fly, the allele that codes for brown body color is represented by a B because brown is the dominant phenotype , and the allele that codes for black body color is represented by a b because black is the recessive phenotype.
As previously mentioned, each fly inherits one allele for the body color gene from each of its parents. Therefore, each fly will carry two alleles for the body color gene. Within an individual organism, the specific combination of alleles for a gene is known as the genotype of the organism, and as mentioned above the physical trait associated with that genotype is called the phenotype of the organism.
So, if a fly has the BB or Bb genotype, it will have a brown body color phenotype Figure 3. In contrast, if a fly has the bb genotype, it will have a black body phenotype.
This outcome shows that the brown allele B and its associated phenotype are dominant to the black allele b and its associated phenotype. Even though all of the offspring have brown body color, they are heterozygous for the black allele.
Figure 8: A Punnett square can help determine the identity of an unknown allele. Brown flies can be either homozygous BB or heterozygous Bb - but is it possible to determine whether a female fly with a brown body has the genotype BB or Bb? To answer this question, an experiment called a test cross can be performed.
Test crosses help researchers determine the genotype of an organism when only its phenotype i. A test cross is a breeding experiment in which an organism with an unknown genotype associated with the dominant phenotype is mated to an organism that is homozygous for the recessive phenotype. The Punnett square in Figure 8 can be used to consider how the identity of the unknown allele is determined in a test cross.
Again, the Punnett squares in this example function like a genetic multiplication table, and there is a specific reason why squares such as these work. During meiosis, chromosome pairs are split apart and distributed into cells called gametes. Each gamete contains a single copy of every chromosome, and each chromosome contains one allele for every gene. Therefore, each allele for a given gene is packaged into a separate gamete.
For example, a fly with the genotype Bb will produce two types of gametes: B and b. In comparison, a fly with the genotype BB will only produce B gametes, and a fly with the genotype bb will only produce b gametes.
Figure A monohybrid cross between two parents with the Bb genotype. Figure Detail The following monohybrid cross shows how this concept works.
The principle of segregation explains how individual alleles are separated among chromosomes. But is it possible to consider how two different genes, each with different allelic forms, are inherited at the same time?
For example, can the alleles for the body color gene brown and black be mixed and matched in different combinations with the alleles for the eye color gene red and brown? The simple answer to this question is yes. When chromosome pairs randomly align along the metaphase plate during meiosis I, each member of the chromosome pair contains one allele for every gene. Each gamete will receive one copy of each chromosome and one allele for every gene. When the individual chromosomes are distributed into gametes, the alleles of the different genes they carry are mixed and matched with respect to one another.
In this example, there are two different alleles for the eye color gene: the E allele for red eye color, and the e allele for brown eye color. The red E phenotype is dominant to the brown e phenotype, so heterozygous flies with the genotype Ee will have red eyes.
Figure The four phenotypes that can result from combining alleles B, b, E, and e. When two flies that are heterozygous for brown body color and red eyes are crossed BbEe X BbEe , their alleles can combine to produce offspring with four different phenotypes Figure Those phenotypes are brown body with red eyes, brown body with brown eyes, black body with red eyes, and black body with brown eyes. Consider a cross between two parents that are heterozygous for both body color and eye color BbEe x BbEe.
This type of experiment is known as a dihybrid cross. All possible genotypes and associated phenotypes in this kind of cross are shown in Figure The four possible phenotypes from this cross occur in the proportions Specifically, this cross yields the following:.
Why does this ratio of phenotypes occur? To answer this question, it is necessary to consider the proportions of the individual alleles involved in the cross. The ratio of brown-bodied flies to black-bodied flies is , and the ratio of red-eyed flies to brown-eyed flies is also This means that the outcomes of body color and eye color traits appear as if they were derived from two parallel monohybrid crosses.
In other words, even though alleles of two different genes were involved in this cross, these alleles behaved as if they had segregated independently. The outcome of a dihybrid cross illustrates the third and final principle of inheritance, the principal of independent assortment , which states that the alleles for one gene segregate into gametes independently of the alleles for other genes.
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