Identifying the sex chromosome in the cattle tick, Rhipicephalus microplus, merging bioinformatics and biology

Sunday, November 13, 2022

8:29 AM – 8:41 AM PT

Location: Vancouver Convention Centre, Meeting Room 212

Presenting Author(s)

Jason Tidwell

Microbiologist
USDA-ARS
Edinburg, Texas

Co-author(s)

JJ

J. Spencer Johnston

Texas A&M University
College Station, Texas

Co-Author(s)

VH

Valerie R. Holmes (she/her/hers)

Graduate Student
Texas A&M University
College Station, Texas

Co-author(s)

KB

Kylie Bendele

USDA-ARS
Kerrville, Texas

Co-Author(s)

Kimberly H. Lohmeyer

Research Entomologist
USDA-ARS
Kerrville, Texas

Co-author(s)

PT

Peter D. Teel

Texas A&M University
College Station, Texas
AT

Aaron Tarone

Professor
Texas A&M University
College Station, Texas

The cattle tick, Rhipicephalus microplus, is one of the most economically important veterinary vectors in the world, costing the agriculture industry billions of dollars annually. Recent control methods in human and other animal vectors have utilized sex determination research to manipulate sex ratios, which has shown promising results with mosquitoes such as Aedes aegypti and Anopheles stephensi. Our study will provide foundational research that will allow similar avenues of investigation in ticks using R. microplus as a model. One of two karyotypes for R. microplus have shown that the largest chromosome is the sex chromosome, and has an XX:XO sex determining system. With flow cytometry, the sex chromosome was estimated at 228.8 Mb. The estimated size did not correlate with the largest chromosome in the genome assembly at 325.14 Mb. Sequencing coverage ratio of mixed sex and male samples against a female reference genome identified two chromosomes with coverages similar to a sex chromosome. SNP density and repeat sequence enrichment analyses corroborated these results identifying chromosomes 2 and 8. Our results suggest that R. microplus could have a complex sex determining system where it has 2 “X” chromosomes, or there may be an error in the current genome assembly. Historical data points to the latter, but it is not unprecedented for spiders and ticks to have complex sex determining systems.