Contrasting effects of geographical separation on the genetic population structure of sympatric species of mites in avocado orchards

Abstract

Oligonychus punicae and Oligonychus perseae (Acari: Tetranychidae) are the most important mite species affecting avocado orchards in Mexico. Here we used nucleotide sequence data from segments of the nuclear ribosomal internal transcribed spacers (ITS1 and ITS2) and mitochondrial cytochrome oxidase subunit I (COI) genes to assess the phylogenetic relationships between both sympatric mite species and, using only ITS sequence data, examine genetic variation and population structure in both species, to test the hypothesis that, although both species co-occur, their genetic population structures are different in both Michoacan state (main producer) and Mexico state. Phylogenetic analysis showed a clear separation between both species using ITS and COI sequence information. Haplotype network analysis done on 24 samples of O. punicae revealed low genetic diversity with only three haplotypes found but a significant geographical population structure confirmed by analysis of molecular variance (AMOVA) and Kimura-2-parameter (K2P) analyses. In addition, a Mantel test revealed that geographical isolation was a factor responsible for the genetic differentiation. In contrast, analyses of 22 samples of O. perseae revealed high genetic diversity with 15 haplotypes found but no geographical structure confirmed by the AMOVA, K2P and Mantel test analyses. We have suggested that geographical separation is one of the most important factors driving genetic variation, but that it affected each species differently. The role of the ecology of these species on our results, and the importance of our findings in the development of monitoring and control strategies are discussed.

Population Genetics ofOligonychus perseae(Acari: Tetranychidae) Collected from Avocados in Mexico and California

“…Thus, it is uncertain whether or not there is overlap in the potential cryptic species reported in the 2 studies. Previously, Guzmán-Valencia et al (2014) detected similar levels of divergence in COI among morphologically identified O. perseae populations from the states of México and Michoacán, but again these specimens were not recognized by the authors as potential cryptic species, nor can we be certain how they relate to ours. Combined, these key studies provide very strong evidence for the existence of a cryptic species complex in O. perseae, and highlight the importance of considering multiple genetic loci in the assessment of such complexes (i.e., not just COI).…”

“…Unfortunately, no molecular data is currently available for O. peruvianus and we were unable to secure authoritatively identified specimens for inclusion in the current study. Ultimately, the insight from our study and Guzmán-Valencia et al (2014 highlight the need to develop and validate unambiguous species identification methods for pest mites infesting avocados (Skoracka et al 2015). Fig.…”

“…tative of Israel, Spain and various regions in Mexico (Ben-David et al 2007;Guzmán-Valencia et al 2014). Examination of COI haplotypes revealed that one, H8, is fixed in California.…”

“…Furthermore, COI sequences can be used to clearly separate O. punicae from O. perseae ( Fig. 2; Guzmán-Valencia et al 2014. Similar, relatively easy, morphological discrimination also can be made between O. yothersi and O. perseae (Ochoa et al 1994) although DNA sequences are not available for the former.…”

“…Maximum likelihood tree constructed from a 305 base pair section of COI using PhyML. Support (aLRT) for major branches is shown.ing patterns: ITS2 sequences from Israel (DQ656456-458;Ben-David et al 2007) and Spain (GU565305; Perez-Sayas et al, unpublished) grouped with COI cluster 1, along with 4 sequences from Mexico (KC568382-385;Guzmán-Valencia et al 2014)…”