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The cascading effects of reinforcement and reproductive character displacement in marine snail sister species

Glenn, Margaret (2018) BIOM01 20171
Degree Projects in Biology
Abstract
Reinforcement is an important process of speciation that may occur when recently diverged lineages come into secondary contact and hybridize. If interspecific mating is costly, selection favors mechanisms that reduce maladaptive hybridization, actively increasing prezygotic isolation between populations and completing speciation. A pattern of reproductive character displacement (RCD) is often used to identify the occurrence of reinforcement. Due to unequal selective pressure between sympatry and allopatry, divergence in mating traits between species is expected to be accentuated in sympatry and less extreme between allopatric heterospecifics. The interaction between species in sympatry may result in such extreme mating traits and... (More)
Reinforcement is an important process of speciation that may occur when recently diverged lineages come into secondary contact and hybridize. If interspecific mating is costly, selection favors mechanisms that reduce maladaptive hybridization, actively increasing prezygotic isolation between populations and completing speciation. A pattern of reproductive character displacement (RCD) is often used to identify the occurrence of reinforcement. Due to unequal selective pressure between sympatry and allopatry, divergence in mating traits between species is expected to be accentuated in sympatry and less extreme between allopatric heterospecifics. The interaction between species in sympatry may result in such extreme mating traits and preferences that sympatric individuals begin to reject allopatric conspecifics. Mating traits that diverge between species in sympatry may therefore result in further reproductive isolation within species, a process known as cascade reinforcement. Mating duration was measured between and within sympatric and allopatric pairs of Littorina fabalis and L. obtusata to identify mate discrimination. Additionally, penis morphology between populations was examined to search for a pattern of RCD. The mating trials did not provide sufficient evidence to support that either reinforcement or cascade reinforcement has occurred in these populations. However, divergence in penial traits was accentuated both between and within species, confirming a pattern of RCD. This pattern of RCD follows the predictions of both reinforcement and cascade reinforcement, suggesting that these processes may yet be key contributors to reproductive isolation between and within L. fabalis and L. obtusata. (Less)
Popular Abstract
A tale of two snails: Genital divergence between populations

There are numerous evolutionary processes that drive speciation and produce the vast diversity of life we see today. Reinforcement is one important process that is said to complete speciation. When two recently diverged sister species come into secondary contact, they may interbreed and form hybrids. However, if these hybrids are unfit or maladapted to the environment, mechanisms may evolve that increase mate discrimination and reduce costly hybridization, effectively completing speciation. Selection against hybrids in overlapping (sympatric) populations may create a pattern where mating traits are accentuated compared to geographically isolated (allopatric) populations. This... (More)
A tale of two snails: Genital divergence between populations

There are numerous evolutionary processes that drive speciation and produce the vast diversity of life we see today. Reinforcement is one important process that is said to complete speciation. When two recently diverged sister species come into secondary contact, they may interbreed and form hybrids. However, if these hybrids are unfit or maladapted to the environment, mechanisms may evolve that increase mate discrimination and reduce costly hybridization, effectively completing speciation. Selection against hybrids in overlapping (sympatric) populations may create a pattern where mating traits are accentuated compared to geographically isolated (allopatric) populations. This pattern is known as reproductive character displacement (RCD) and is a signature of reinforcement. The interaction between species in sympatry may result in the evolution of such extreme mating traits and preferences that sympatric individuals begin to reject potential allopatric mates of their same species that no longer meet their mating criteria. Mating traits that diverge between species in sympatry may therefore result in further reproductive isolation within species, a process known as cascade reinforcement.

I investigated the cascading effects of reinforcement in the flat periwinkles Littorina fabalis and L. obtusata, two marine sister snail species found across Europe. I conducted mating experiments between and within sympatric and allopatric populations of L. fabalis and L. obtusata to determine if and how these populations discriminate against mates from other populations. Mating duration was used to signify sperm transfer and therefore the potential for offspring. If reinforcement and cascade reinforcement had occurred, I expected shorter mating between the sympatric species well as shorter mating between sympatric and allopatric populations of the same species.

Additionally, penis morphology between populations was examined to search for a pattern of RCD and a possible mechanism of mate discrimination. Penis morphology is very diverse in Littorina species and has proven reliable for species identification. Genital divergence has previously been demonstrated as a result of reinforcement to increase reproductive isolation and improve mate discrimination. Therefore, RCD of penis morphology in these snails was evaluated to explain a possible means of mate discrimination during copulation.

The mating trials did not provide sufficient evidence to support that either reinforcement or cascade reinforcement has occurred in these populations. However, divergence in penial traits was accentuated both between and within species, confirming a pattern of RCD. This pattern of RCD follows the predictions of both reinforcement and cascade reinforcement, suggesting that these processes may yet be key contributors to reproductive isolation between and within L. fabalis and L. obtusata. Whether this displacement in genital morphology has an impact on the mating preferences of sympatric L. fabalis and L. obtusata remains unanswered. However, based on the trends in mating duration observed between pairs, the possibility of reinforcement and cascade reinforcement in L. fabalis and L. obtusata persists.

Master’s Degree Project in Biology, 30 credits, 2017
Department of Biology, Lund University

Advisor: Johan Hollander
Aquatic Ecology, Department of Biology; Lund University (Less)
Please use this url to cite or link to this publication:
author
Glenn, Margaret
supervisor
organization
course
BIOM01 20171
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8932026
date added to LUP
2018-01-12 14:43:47
date last changed
2018-01-12 14:43:47
@misc{8932026,
  abstract     = {Reinforcement is an important process of speciation that may occur when recently diverged lineages come into secondary contact and hybridize. If interspecific mating is costly, selection favors mechanisms that reduce maladaptive hybridization, actively increasing prezygotic isolation between populations and completing speciation. A pattern of reproductive character displacement (RCD) is often used to identify the occurrence of reinforcement. Due to unequal selective pressure between sympatry and allopatry, divergence in mating traits between species is expected to be accentuated in sympatry and less extreme between allopatric heterospecifics. The interaction between species in sympatry may result in such extreme mating traits and preferences that sympatric individuals begin to reject allopatric conspecifics. Mating traits that diverge between species in sympatry may therefore result in further reproductive isolation within species, a process known as cascade reinforcement. Mating duration was measured between and within sympatric and allopatric pairs of Littorina fabalis and L. obtusata to identify mate discrimination. Additionally, penis morphology between populations was examined to search for a pattern of RCD. The mating trials did not provide sufficient evidence to support that either reinforcement or cascade reinforcement has occurred in these populations. However, divergence in penial traits was accentuated both between and within species, confirming a pattern of RCD. This pattern of RCD follows the predictions of both reinforcement and cascade reinforcement, suggesting that these processes may yet be key contributors to reproductive isolation between and within L. fabalis and L. obtusata.},
  author       = {Glenn, Margaret},
  language     = {eng},
  note         = {Student Paper},
  title        = {The cascading effects of reinforcement and reproductive character displacement in marine snail sister species},
  year         = {2018},
}