Gertrud Theiler Tick Museum - Epidemiology, Parasites and Vectors, Agricultural Research Council - Onderstepoort Veterinary Research, Pretoria 0110, South Africa; Evolutionary Genomics Group, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa.
Evolutionary Genomics Group, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa; Middlesex University, Department of Natural Sciences- Faculty of Science and Technology, London NW4 4BT, United Kingdom.
Mol Phylogenet Evol. 2021 Sep;162:107178. doi: 10.1016/j.ympev.2021.107178. Epub 2021 Apr 20.
Rhipicephalus are a species-diverse genus of ticks, mainly distributed in the Afrotropics with some species in the Palearctic and Oriental regions. Current taxonomic consensus comprise nine informal species groups/lineages based on immature morphology. This work integrates biogeographic, ecological and molecular lines of evidence to better understand Rhipicephalus evolution. Phylogenetic analysis based on four genes (12S, 16S, 28S-D2 and COI) recovered five distinct clades with nine descendant clades that are generally congruent with current taxonomy, with some exceptions. Historical biogeography is inferred from molecular divergence times, ancestral distribution areas, host-use and climate niches of four phylogenetically significant bioclimatic variables (isothermality, annual, seasonal and diurnal temperature range). Novel hosts enabled host-linked dispersal events into new environments, and ticks exploited new hosts through nested predator-prey connections in food webs. Diversification was further induced by climate niche partitioning along gradients in temperature range during off-host periods. Ancestral climate niche estimates corroborated dispersal events by indicating hypothetical ancestors moved into environments with different annual and seasonal temperature ranges along latitudinal gradients. Host size for immature and adult life stages was important for dispersal and subsequent diversification rates. Clades that utilise large, mobile hosts (ungulates and carnivores) early in development have wider geographic ranges but slower diversification rates, and those utilising small, less mobile hosts (rodents, lagomorphs and afroinsectivores) early in development have smaller ranges but higher diversification rates. These findings suggest diversification is driven by a complex set of factors linked to both host-associations (host size, ranges and mobility) and climate niche partitioning along annual and seasonal temperature range gradients that vary with latitude. Moreover, competitive interactions can reinforce these processes and drive speciation. Off-host periods facilitate adaptive radiation by enabling host switches along nested predator-prey connections in food webs, but at the cost of environmental exposure that partitions niches among dispersing progenitors, disrupting geneflow and driving diversification. As such, the evolution and ecological niches of Rhipicephalus are characterised by trade-offs between on- and off-host periods, and these trade-offs interact with nested predator-prey connections in food webs, host-use at different life stages, as well as gradients in annual and seasonal temperature ranges to drive adaptive radiation and speciation.
硬蜱是蜱属的一个物种多样性丰富的属,主要分布在热带非洲,有些物种分布在古北界和东洋界。目前的分类共识包括基于若虫形态的九个非正式的种组/谱系。这项工作整合了生物地理、生态和分子证据线,以更好地了解硬蜱的进化。基于四个基因(12S、16S、28S-D2 和 COI)的系统发育分析,恢复了五个不同的分支,有九个后裔分支,通常与当前的分类学一致,但也有一些例外。分子分歧时间、祖先分布区、宿主利用和气候生境(四个系统发育上有意义的生物气候变量:等温性、年、季节和昼夜温度范围)的历史生物地理学是从分子分歧时间、祖先分布区、宿主利用和气候生境推断出来的。宿主连接的扩散事件使新的宿主能够进入新的环境,而蜱则通过食物网中的嵌套捕食者-猎物关系利用新的宿主。在非宿主期,温度范围的梯度导致气候生境的划分,进一步促进了多样化。祖先气候生境估计通过表明假设的祖先沿着纬度梯度移动到具有不同年和季节温度范围的环境中,证实了扩散事件。若虫和成虫生命阶段的宿主大小对于扩散和随后的多样化速度很重要。那些在发育早期利用大型、移动宿主(有蹄类和食肉动物)的分支具有更广泛的地理范围,但多样化速度较慢,而那些在发育早期利用小型、移动性较差的宿主(啮齿动物、兔形目动物和非洲食虫动物)的分支则具有较小的范围,但多样化速度较快。这些发现表明,多样化是由一系列与宿主相关联的复杂因素驱动的(宿主大小、范围和移动性),以及沿着年和季节温度范围梯度的气候生境划分,这些梯度随纬度而变化。此外,竞争相互作用可以加强这些过程并推动物种形成。非宿主期通过在食物网中嵌套的捕食者-猎物连接促进宿主转换,从而促进适应性辐射,但代价是暴露于环境中,这会导致扩散后代之间的生态位划分,破坏基因流并促进多样化。因此,硬蜱的进化和生态位是以宿主的生境为特征的,这种生境的特征是在生境和非生境之间存在权衡,而这些权衡与食物网中的嵌套捕食者-猎物连接、不同生命阶段的宿主利用以及年和季节温度范围的梯度相互作用,以驱动适应性辐射和物种形成。
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