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The influence of tick behavior, biotope and host specificity on concerted evolution of the platelet aggregation inhibitor savignygrin, from the soft tick Ornithodoros savignyi.

Abstract：

:Ticks are obligate blood-feeding parasites that secrete anti-hemostatic components during feeding to enable control of the hemostatic system of the host. Complex interactions at the tick-host interface are an indication of the important role that the host played during tick evolution. The question is to what extent interaction with the host and the environment influences tick evolution. Previously, two isoforms (97% sequence identity) of savignygrin, an alphaIIbbeta3 antagonist, have been described. The presence of both isoforms within 20 random individuals confirmed that these isoforms must be recent gene duplicates. Analysis of the sequence differences between the isoforms shows a Kn/Ks ratio of 1, which indicates neutral selection for the isoforms. However, the biased localization of differences within the 3' end of the genes suggests that concerted evolution acts on the isoforms. Calculation of the divergence date between the isoforms (1.6-5.2 MYA) also indicates purifying selection, as ample time had passed after duplication, for inactivation of one gene copy. We conclude that concerted evolution has functioned to maintain a high copy number of the savignygrins in order for Ornithodoros savignyi to parasitize a wide host range. This contrasts with O. moubata that expresses the savignygrin homolog, disagregin, as a single copy at lower concentration levels and correlates with the confined habitat and consequently narrow host range of O. moubata. Recent "domestication" of O. savignyi due to animal husbandry practices could however, have reduced the selection constraints acting to maintain the gene copies as evidenced by the structural instability of one of the isoforms. Our results suggest that environmental factors and host associations do play an important role in the evolution of anti-hemostatic components in ticks.

journal_name

Insect Biochem Mol Biol

journal_title

Insect biochemistry and molecular biology

authors

Mans BJ,Louw AI,Neitz AW

doi

10.1016/s0965-1748(03)00047-x

subject

Has Abstract

pub_date

2003-06-01 00:00:00

pages

623-9

issue

eissn

0965-1748

issn

1879-0240

pii

S096517480300047X

journal_volume

pub_type

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The influence of tick behavior, biotope and host specificity on concerted evolution of the platelet aggregation inhibitor savignygrin, from the soft tick Ornithodoros savignyi.