Effects of Mating System on Accessory Gland Protein Evolution in Heliconius Butterflies

EFFECTS OF MATING SYSTEM ON ACCESSORY GLAND PROTEIN EVOLUTION IN HELICONIUS BUTTERFLIES

Sponsoring Institution

State Agricultural Experiment Station

Project Status

TERMINATED

Funding Source

STATE

Reporting Frequency

Annual

Accession No.

0208033

Grant No.

(N/A)

Project No.

NYC-183336

Proposal No.

(N/A)

Multistate No.

(N/A)

Program Code

(N/A)

Project Start Date

Jul 1, 2006

Project End Date

Sep 30, 2009

Grant Year

(N/A)

Project Director
Harrison, R. G.

Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853

Performing Department
ECOLOGY & EVOLUTIONARY BIOLOGY

Non Technical Summary
Proteins directly involved in fertilization in sexually reproducing animals are often unusually divergent when compared between closely related species. The reasons for this rapid divergence are currently not well understood. This research critically examines the hypothesis that rapid genetic change is a consequence of competition among males for opportunities to fertilize females.

Animal Health Component

(N/A)

Research Effort Categories

Basic

100%

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
301	3110	1070	10%
304	3110	1040	45%
304	3110	1080	45%

Knowledge Area
301 - Reproductive Performance of Animals; 304 - Animal Genome;

Subject Of Investigation
3110 - Insects;

Field Of Science
1070 - Ecology; 1080 - Genetics; 1040 - Molecular biology;

Keywords

expressed sequence tag

est

monandry

polyandry

Goals / Objectives
We will identify accessory gland protein (ACP) genes and describe their patterns of evolution in Heliconius butterflies with divergent mating systems. We will examine the effect of post-copulatory sexual selection (PCSS) on ACP evolution by contrasting patterns of selection and divergence between species with different mating system. Specific objectives are: 1) Isolate and characterize male ACP genes from Heliconius butterflies; concomitantly identify non-reproductive proteins for comparison to ACPs. 2) Obtain sequences from ACP and non-reproductive protein genes from several species representing each mating system. 3) Quantify and compare patterns of divergence and selective pressures between: a) ACP genes vs. non-reproductive protein genes b) Pupal mating vs. adult mating species, focusing on ACPs.

Project Methods
Expressed sequence tags (ESTs) will be generated from cDNA libraries of male accessory glands from two species that are representative of the two distinct mating systems found in the genus: H. erato (pupal mating) and H. melpomene (adult mating). These EST data, combined with bioinformatic analyses and experiments assaying tissue-specific patterns of gene expression (e.g. RT-PCR), will be used to identify and characterize accessory gland protein (ACP) genes and non-reproductive protein genes. Once identified, PCR primers will be designed and used to amplify these genes out of several species from four pupal mating species (H. erato, H. hewitsoni, H. sara, H charithonia), four species representing a derived adult mating clade (H. melpomene, H. pachinus, H. hecale, H. numata), and one primitive adult mating species (H. wallacei) which will serve as an outgroup. The sequence data from multiple species will be analyzed with maximum likelihood methods implemented in the software package PAML. The parameters (e.g. dN, dS, w) required for evolutionary comparisons can be estimated from pairwise comparisons between two lineages as well as from multiple lineages in a phylogenetic framework. Using data from multiple lineages allows detection of variation both in evolutionary rates among branches in a phylogeny and among different codons in a gene. Specifically, PAML estimates how well different models of molecular evolution fit a given phylogeny. These models are nested and the relative goodness-of-fit can be evaluated with a likelihood ratio test. This framework also provides a sensitive means of identifying adaptive molecular evolution. Variation in evolutionary rates between groups of genes will be tested statistically using random permutation tests. Permutation tests compare an observed parameter to a null distribution obtained by repeatedly randomly reordering the data. This method of statistical inference has the advantage of not making any a priori assumptions about the distribution of the parameters (dN, dS, w) estimated from the sampled loci and is particularly appropriate with unequal and small sample sizes. Using permutation tests to compare parameter estimates obtained from PAML, we will test specific predictions about the evolution of ACPs, both in relation to other groups of proteins as well as between mating system. If post-copulatory sexual selection drives the rapid, adaptive evolution of reproductive proteins, then we expect to observe greater divergence and adaptive evolution among ACP genes associated with the adult mating clade.

Progress 07/01/06 to 09/30/09

Outputs
OUTPUTS: Using current genomic and proteomic approaches, we have demonstrated that proteins transferred from males to females in the seminal fluid of Heliconius butterflies are rapidly evolving relative to a large group of control proteins expressed in wing disc. Our approach has been to compare the results of proteomic analysis of male spermatophore contents with sequences from Heliconius accessory gland libraries. For some proteins, this rapid evolution results from positive selection among species in the clade with promiscuous mating behavior. However, on average, protein evolution is faster among monandrous, pupal-mating butterflies. This is an unexpected result but might be explained by relaxed constraint following a evolutionary transition in mating systems. We have reported these results by presenting talks and posters at local, regional, and international scientific meetings. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
These findings have implications for understanding what causes the broadly observed pattern of elevated divergence among genes with reproductive function. In particular, it is the first time such an observation has been made in butterflies. Also, because of the mating system these butterflies have, this observation indicates that models of sexual antagonism insufficiently explain all instances of elevated divergence among reproductive proteins.

Publications

No publications reported this period

Progress 10/01/07 to 09/30/08

Outputs
OUTPUTS: We have identified several genes corresponding to proteins, which are transferred from males to females in the seminal fluid of Heliconius butterflies. On average, these genes appear to be diverging faster than other genes in the Heliconius genome. We have reported these results by presenting talks and posters at local, regional, and international scientific meetings. PARTICIPANTS: James Walters is a graduate student who is working on this project as part of his Ph.D. thesis. TARGET AUDIENCES: Population geneticists, evolutionary biologists. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
These findings have implications for understanding what causes the broadly observed pattern of elevated divergence among genes with reproductive function. In particular, it is the first time such an observation has been made in butterflies. Also, because of the mating system these butterflies have, this observation indicates that models of sexual antagonism insufficiently explain all instances of elevated divergence among reproductive proteins.

Publications

Papa, R., Morrison, C.M., Walters, J.R., Counterman, B.A., Chen, R., Halder, G., Roberts, L., Kapan, D.D., Jiggins, C.D., Reed, R.D., and McMillan, W.O. 2008. Highly conserved gene order and numerous novel repetitive elements in genomic regions linked to wing pattern variation in Heliconius butterflies. BMC Genomics 9:345.
Walters, J.R. and Harrison, R.G. 2008. EST analysis of male accessory glands from Heliconius butterflies with divergent mating systems. BMC Genomics 9:592.

Progress 10/01/06 to 09/30/07

Outputs
We have identified several genes corresponding to proteins, which are transferred from males to females in the seminal fluid of Heliconius butterflies. On average, these genes appear to be diverging faster than other genes in the Heliconius genome. We have reported these results by presenting talks and posters at local, regional, and international scientific meetings.

Impacts
These findings have implications for understanding what causes the broadly observed pattern of elevated divergence among genes with reproductive function. In particular, it is the first time such an observation has been made in butterflies. Also, because of the mating system these butterflies have, this observation indicates that models of sexual antagonism insufficiently explain all instances of elevated divergence among reproductive proteins.

Publications

No publications reported this period

Progress 01/01/06 to 12/31/06

Outputs
Proteins, which are directly involved in fertilization in sexually reproducing animals, are often unusually divergent when compared between closely related species. The reasons for rapid divergence, observed in organisms ranging from mollusks to mammals, are currently not well understood. This project critically examines the hypothesis that rapid genetic change is a consequence of competition among males for opportunities to fertilize females. The proposed research focuses on Heliconius butterflies (a group of insects with a long history in genetic research) and has two major goals: (1) to identify genes encoding proteins involved in fertilization and egg laying and (2) to compare patterns of divergence in these genes between species with different mating systems, i.e., different levels of competition among males. If mating system influences rates of molecular change, levels of genetic divergence among reproductive proteins should correlate with mating system. Understanding the nature and causes of changes in proteins that mediate interactions between sperm and egg will provide important insights into the origin of diversity (how new species arise). In addition, examining unusual patterns of genetic divergence between species will also offer important insights into biological function, with implications for medicine, agriculture, and the environment. Ultimately, determining the cause of the unusual divergence found among reproductive proteins will help to inform efforts to control insect pests and treat infertility.

Impacts
Proteins directly involved in fertilization in sexually reproducing animals are often unusually divergent when compared between closely related species. The reasons for this rapid divergence are currently not well understood. This research critically examines the hypothesis that rapid genetic change is a consequence of competition among males for opportunities to fertilize females.

Publications

No publications reported this period