Question

2) Consider the large ground finch (Geospiza magnirostris) and the medium ground finch (Geospiza fortis). The males of these two species have different calls to attract females. These two species exist together on some islands (sympatric) but each also exist on some islands alone (allopatric). (12 points) a) In which populations do you think it is more likely to observe strong prezygotic reproductive isolation when attempting to hybridize these finches in the lab?(circle one)

Sympatric populations or Allopatric populations

b) Explain the reasons for your expectation in (a). In your answer, be sure to fully explain the underlying reason you expect prezygotic isolation to be stronger in one set of populations versus the other and discuss how you expect hybridization to affect the fitness of the parents and the resulting offspring involved in a hybridization event, being specific to these two species of ground finches.

Answer 1

Pre-zygotic reproductive isolation is the most of the natural selection of a population, as resources are not wasted on the production. These mechanisms include physiological or systemic barriers to fertilization. If a species is defined as a group of potentially interbreeding populations, according to different anatomy, behavior, time available for mating, or some other barrier that separates populations into species, can be categorized whether the barrier blocks fertilization (a prezygotic barrier) and a postzygotic barrier.

Prezygotic barriers to reproduction include habitat, timing, behavior, and gametic isolation; any barrier that functions before a zygote is formed.

Geospiza fortis, the medium ground finch, is a granivorous bird with a short and blunt beak and Geospiza magnirostris, the large-beaked ground finch, feeds on large and hard seeds. Three factors contribute to the barrier for interbreeding and an exchange of genes between Darwin's finch species: differences in song, morphology and ecological conditions during the dry season. The barrier breaks down with a simultaneous weakening of the differences. They hybridize when individuals learn the song of another species and morphological differences between them are small. When ecological conditions are suitable for the survival hybrids they backcross to the parental species.

Hybridization is indicated by the greater genetic similarity of sympatric populations of species than allopatric populations of the same species. Different symbols indicate different combinations of species of large ground finches and medium ground finches.

Several mechanisms that play a role in interbreeding.  Allopatric speciation occurs when populations become physically isolated due to some sort of geographical barrier. Sympatric speciation occurs when populations become genetically isolated, not even physically separation is mandatory.

Sympatric speciation is speciation in the absence of geographic separation. Whereas the Allopatric speciation involves some sort of geographical isolation that physically blocks migration. Geographical isolation may result from the changes in the path of a river, the uplift of a mountain range, the formation of a canyon, or other landmass changes.

Sympatric speciation occurs without a physical barrier to gene flow. This is more common in plant species, although it also has been documented in a few animals. Due to errors in cell division to produce gametes with an extra set of chromosomes if the homologous pairs are not separated in Meiosis. If a plant is able to self-fertilize, the union of two of these unreduced gametes results is a condition called polyploidy.

to support the argument that allopatric population is likely to observe stronger:

• Closely related species pairs, more often than not, reside in geographic ranges adjacent to one another, separated by a geographic or climatic barrier.
• Young species pairs or sister species often occur in allopatry, even without a known barrier.
• Measures of reproductive isolation increase with the greater geographic distance of separation between two species pairs.
• In regions where geographic isolation is doubtful, species do not exhibit sister pairs.?

Fitness is a term that has a precise biological meaning - reproductive success. In simplest terms, an individual who produces four offspring is relatively more fit than one who produces three offspring. The individual producing four fit offspring contributes 25% more of their genes to the next generation than the individual producing three fit offspring. Fitness can be quantified in small populations because the survival and reproductive fates of offspring can be documented. Fitness varies as a result of habitat change caused by extreme interannual climatic fluctuations.