Question

Sexual selection favors individuals with traits that increase their ability to obtain mates, such as mating calls in crickets. Using this example, propose a scenario where sexual selection could contribute to divergence in sympatric speciation.

Short answer

In a population of crickets living in the same geographic area, variation in the frequency and pattern of male mating calls exists. Female crickets prefer specific tones and rhythms, leading to reproductive success for males with preferred calls. Over time, reproductive isolation occurs as two groups form based on mating call preferences, and genetic differences accumulate. Through genetic drift and natural selection, further divergence in traits such as size, color, and habitat preference leads to the formation of two distinct species coexisting within the same geographic area, exemplifying sympatric speciation driven by sexual selection.

Step-by-step solution

Understand the concept of sexual selection

Sexual selection is a type of natural selection where individuals with certain traits increase their chances of obtaining mates. In other words, the individuals who possess traits that are more attractive to the opposite sex will have more opportunities to reproduce, passing on their advantageous traits to the next generation.

Understand the concept of sympatric speciation

Sympatric speciation is the process by which new species evolve from a single ancestral species within the same geographic area. This type of speciation occurs when populations become reproductively isolated from each other due to differences in mating preferences or other factors, resulting in genetic divergence and the formation of new species.

Identify the role of mating calls in crickets

In the given example, mating calls in crickets serve as a means of attracting mates. Female crickets are attracted to certain frequencies and patterns of sound produced by male crickets' chirping. In this context, mating calls are subjected to sexual selection, favoring individuals with more successful calls in terms of attracting females.

Propose a scenario involving sexual selection and sympatric speciation

Imagine a population of crickets living in the same geographical area. Within this population, there is variation in the frequency and pattern of male cricket mating calls. Females display preferences for specific tones and rhythms, which leads to more successful mating and reproduction for males with those preferred calls. As time goes on, this preference causes the population to split into two distinct groups based on the preference for different mating calls. The two groups of crickets no longer interbreed, as females from each group are not attracted to the mating calls of males from the other group. This reproductive isolation leads to the accumulation of genetic differences between the two groups.

Divergence through natural selection and genetic drift

Over time, and without interbreeding, these two groups of crickets will experience genetic drift and other forms of natural selection, potentially leading to further divergence in other traits, such as size, color, or habitat preference. These differences accumulate over time, eventually leading to the formation of two distinct species of crickets, both existing within the same geographic area—a case of sympatric speciation driven by sexual selection.

Key concepts

Sympatric Speciation

Sympatric speciation is a fascinating process where new species arise from a single ancestral species, all while sharing the same geographical location. Unlike allopatric speciation, where physical barriers lead to species divergence, sympatric speciation occurs without such barriers.
This process can be driven by various factors, including ecological, behavioral, or genetic differences within a population.
For example, the preference for specific mating calls among crickets can cause reproductive isolation within the same environment. In sympatric speciation, one key element is that the populations become reproductively isolated.
This means that even though they live in the same area, members of these groups do not mate with each other. This can be due to differences in mating preferences, like those seen in crickets where females prefer certain mating calls.
Over time, these isolated groups diverge genetically, eventually leading to the emergence of new species.

Mating Calls in Crickets

Mating calls in crickets are fascinating examples of how sexual selection operates. Male crickets produce chirping sounds by rubbing their wings together. These sounds serve as mating calls to attract female crickets.
Different species and even groups within species often have distinct mating call patterns, which include variations in frequency and rhythm. Female crickets tend to be choosy, showing preferences for specific patterns that indicate a healthy or fit mate. Due to these preferences, mating calls are subject to a form of sexual selection. Males with more appealing calls are more likely to attract a mate and successfully reproduce.
As a result, these males pass on their genes to the next generation, ensuring that their mating calls become more common in the population. This selection pressure can lead to notable changes in a population over time, especially if different groups prefer different calls, setting the stage for sympatric speciation.

Reproductive Isolation

Reproductive isolation is a crucial element in the process of forming new species, particularly in sympatric speciation. When populations inhabit the same area but do not interbreed, they become reproductively isolated.
This separation can result from various factors like differing mating preferences, temporal differences in breeding, or even mechanical barriers. In crickets, reproductive isolation often occurs due to differences in mating calls. If female crickets prefer one type of call over another, males producing less-preferred calls will have reduced chances of mating.
This can gradually lead to a division in the population, where two distinct groups emerge that do not interbreed. Without interbreeding, these groups start to accumulate genetic differences, leading them down the path towards becoming separate species.
Reproductive isolation ensures that genetic material is not exchanged between the diverging groups, allowing them to evolve independently. This illustrates how behavioral factors, like mating calls, contribute to reproductive isolation.

Genetic Divergence

Genetic divergence is the process by which two or more populations of a species accumulate genetic differences over time. These differences can become significant enough to result in the formation of new species.
In the context of sympatric speciation, genetic divergence often stems from reproductive isolation, where isolated populations no longer exchange genes with one another. Among crickets, genetic divergence can be facilitated by differences in mating calls. As male crickets with certain calls reproduce more successfully, their genes become more prevalent in the population.
Over generations, these genetic changes can influence other traits beyond just mating calls, such as body size, color, or habitat preferences. As these genetic changes accumulate, the genetic divergence between groups can be significant enough to establish them as distinct species, even though they all started from a common ancestral group and share the same environment. Thus, genetic divergence is a critical outcome and driver of sympatric speciation, where behavioral traits play a significant role in the genetic evolution of species.