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Types of Selection

Types of Selection

Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...

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Predator-Prey Interactions

Predators consume prey for energy. Predators that acquire prey and prey that avoid predation both increase their chances of survival and reproduction (i.e., fitness). Routine predator-prey interactions elicit mutual adaptations that improve predator offenses, such as claws, teeth, and speed, as well as prey defenses, including crypsis, aposematism, and mimicry. Thus, predator-prey interactions resemble an evolutionary arms race.

Convergent Evolution

Convergent Evolution

Evolution shapes the features of organisms over time, ensuring that they are suited for the environments in which they live. Sometimes, selection pressure leads to the rise of similar but unrelated adaptations in organisms with no recent common ancestors, a process known as convergent evolution.

Cis-regulatory Sequences

Cis-regulatory Sequences

Cis-regulatory sequences are short fragments of non-coding DNA that are present on the same chromosomes as the genes that they regulate. These fragments serve as binding sites for transcriptional regulators, proteins that are responsible for controlling gene transcription and differential gene expression across cell types in eukaryotes. Cis-regulatory sequences can be close to the gene of interest or thousands of bases away in the DNA sequence; however, those sequences that are further away are...

Frequency-dependent Selection

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.

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Related Experiment Video

Updated: May 21, 2025

Extraction of Venom and Venom Gland Microdissections from Spiders for Proteomic and Transcriptomic Analyses

Extraction of Venom and Venom Gland Microdissections from Spiders for Proteomic and Transcriptomic Analyses

Published on: November 3, 2014

A Segregating Structural Variant Defines Novel Venom Phenotypes in the Eastern Diamondback Rattlesnake.

Pedro G Nachtigall^1,2, Gunnar S Nystrom¹, Emilie M Broussard¹

¹Department of Biological Science, Florida State University, Tallahassee, FL, USA.

Molecular Biology and Evolution

|March 18, 2025

Summary

Structural variants drive venom evolution in rattlesnakes. A large deletion of snake venom metalloproteinase (SVMP) genes in Crotalus adamanteus creates unique venom phenotypes, independent of myotoxin (MYO) variation.

Keywords:

conservation genomics rattlesnake structural variation venom

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Area of Science:

Evolutionary Biology
Genomics
Biochemistry

Background:

Structural variants are key drivers of phenotypic variation, yet challenging to identify.
Snake venom composition exhibits significant intraspecific variation, with parallel evolution of neurotoxic venoms observed in rattlesnakes.
This evolution involves deletion of snake venom metalloproteinase (SVMP) toxins and recruitment of phospholipase A2 (PLA2) toxins.

Purpose of the Study:

To investigate the role of structural variation in shaping venom phenotypes in the eastern diamondback rattlesnake (Crotalus adamanteus).
To identify specific genetic mechanisms, such as gene deletions, contributing to venom variation within this species.
To understand the geographic distribution and evolutionary implications of identified structural variants.

Main Methods:

Generation of a haplotype-resolved, chromosome-level genome assembly for Crotalus adamanteus.
Population-genomic analysis to assess the frequency and distribution of structural variants across the species' range.
Genotyping of SVMP and myotoxin (MYO) genes to correlate with venom phenotypes.

Main Results:

Discovery of a large (∼225 Kb) deletion encompassing six SVMP genes in C. adamanteus, mirroring a key step in neurotoxic venom evolution.
Identification of this SVMP deletion as the dominant homozygous genotype in the vulnerable northwestern periphery of the species' range.
Demonstration that SVMP deletions and MYO copy number variation are genetically independent, leading to novel venom phenotypes across the geographic range.

Conclusions:

Structural variation, specifically large gene deletions, is a primary determinant of geographic venom variation in C. adamanteus.
C. adamanteus exhibits a unique evolutionary trajectory, deleting SVMP genes without concurrently recruiting neurotoxic PLA2s.
The independent variation of SVMP and MYO genotypes results in a diverse array of venom phenotypes, highlighting the complex evolutionary pathways in rattlesnake venom.