Genetic insights into the globally invasive and taxonomically problematic tree genus Prosopis

Accurate taxonomic identification of alien species is crucial to detect new incursions, prevent or reduce the arrival of new invaders and implement management options such as biological control. Globally, the taxonomy of non-native Prosopis species is problematic due to misidentification and extensive hybridization. We performed a genetic analysis on several Prosopis species, and their putative hybrids, including both native and non-native populations, with a special focus on Prosopis invasions in Eastern Africa (Ethiopia, Kenya and Tanzania). We aimed to clarify the taxonomic placement of non-native populations and to infer the introduction histories of Prosopis in Eastern Africa. DNA sequencing data from nuclear and chloroplast markers showed high homology (almost 100%) between most species analysed. Analyses based on seven nuclear microsatellites confirmed weak population genetic structure among Prosopis species. Hybrids and polyploid individuals were recorded in both native and non-native populations. Invasive genotypes of P. juliflora in Kenya and Ethiopia could have a similar native Mexican origin, while Tanzanian genotypes likely are from a different source. Native Peruvian Prosopis pallida genotypes showed high similarity with non-invasive genotypes from Kenya. Levels of introduced genetic diversity, relative to native populations, suggest that multiple introductions of P. juliflora and P. pallida occurred to Eastern Africa. Polyploidy may explain the successful invasion of P. juliflora in Eastern Africa. The polyploid Prosopis juliflora was highly differentiated from the rest of the (diploid) species within the genus. The lack of genetic differentiation between most diploid species in their native ranges supports the notion that hybridization between allopatric species may occur frequently when they are co-introduced into non-native areas. For regulatory purposes, we propose to treat diploid Prosopis taxa from the Americas as a single taxonomic unit in non-native ranges.

Methods
Eleven previously-published nuclear microsatellite loci were amplified in a variety of Prosopis species. Amplified fragments were submitted for gel capillary electrophoresis at Stellenbosch University’s Central Analytical Facility. Automated allele scoring was done using the GeneMarker version 2.6.4 software (SoftGenetics LLC, Pennsylvania, United States) and all alleles were manually checked. The data is provided in GenAlex format (Peakall and Smouse 2012).

Reference: Peakall, R. and Smouse P.E. (2012) GenAlEx 6.5: genetic analysis in Excel. Population genetic software for teaching and research-an update. Bioinformatics 28, 2537-2539.

Usage Notes
Missing data (alleles) are indicated as 0's. A separate tab in the spreadsheet provide metadat on location and species identities.

精确鉴定外来物种的分类学对于检测新入侵、预防或减少新入侵者的到来以及实施生物控制等管理措施至关重要。在全球范围内，由于误鉴定和广泛的杂交，非本地 Prosopis 物种的分类学存在难题。我们对多种 Prosopis 物种及其潜在杂交种进行了遗传分析，包括本地和非本地种群，特别关注东非（埃塞俄比亚、肯尼亚和坦桑尼亚）的 Prosopis 入侵情况。我们的目标是阐明非本地种群的分类学位置，并推断 Prosopis 在东非的引入历史。来自核和叶绿体标记的 DNA 测序数据表明，大多数分析物种之间具有较高的同源性（几乎达到100%）。基于七个核微卫星的分析证实了 Prosopis 物种之间微弱的种群遗传结构。在本地和非本地种群中均记录了杂交个体和多倍体个体。肯尼亚和埃塞俄比亚的 P. juliflora 侵袭基因型可能具有类似的本地墨西哥起源，而坦桑尼亚基因型可能来自不同的来源。原生秘鲁 Prosopis pallida 基因型与肯尼亚的非侵袭基因型具有高度相似性。相对于本地种群，引入的遗传多样性水平表明，P. juliflora 和 P. pallida 在东非发生了多次引入。多倍性可能解释了 P. juliflora 在东非的成功入侵。多倍体 Prosopis juliflora 与该属中其他（二倍体）物种高度分化。大多数二倍体物种在其原生范围内的遗传分化不足支持了这样的观点：当它们共同引入非本地区域时，地理隔离物种之间的杂交可能频繁发生。为了监管目的，我们建议将来自美洲的二倍体 Prosopis 分类单元在非本地区域视为一个单一的分类单元。