Massive Extraction of the Orchid Laelia speciosa (HBK) Schltr. for Trading in Local Markets Affect Its Population Genetic Structure in a Fragmented Landscape in Central Mexico

Abstract

Laelia speciosa is an orchid species listed as threatened of extinction in the Mexican standard NOM-059. Wild populations of L. speciosa have been declining due to fragmentation of its habitat and massive extraction for trading in local markets in Mexico. In this study, we aimed to evaluate the evolutionary potential of L. speciosa within a fragmented landscape of ca. 4000 km 2 in the Cuitzeo basin, State of Michoacán. We sampled 15 populations throughout the Cuitzeo basin and amplified eight nuclear microsatellite markers to assess genetic diversity, structure, and connectivity and to test for evidence of recent bottlenecks. Surprisingly, L. speciosa populations showed high genetic diversity, with values ranging from moderate to high compared with those reported for other orchid species. Also, the analysis of molecular variance and R ST results indicated the existence of low genetic differentiation, favored by its cross pollination habit which facilitates the maintenance of gene flow and that have been observed in other orchid species. Wright's within-population inbreeding (F IS ) was positive in all cases, denoting a heterozygosity deficit, with moderate-to-high values. Fragmentation may also lead to inbreeding due to either increased self-fertilization or mating between related individuals within remnant fragments. The L. speciosa populations examined showed evidence suggesting that some populations had recently gone through a bottleneck. We also observed that all the L. speciosa populations had a moderate effective population size. The history of L. speciosa in the Cuitzeo basin suggests that both fragmented and non-fragmented populations may have been recently subject to moderate reductions in effective population size, large enough to affect their allelic diversity, F IS , but not their H E . Such reductions may have been caused by episodic environmental fluctuations or resulted from the recent founding of some of the populations. The effective population size can be used as an indicator of habitat quality, and this was confirmed for the L. speciosa populations, which have undergone a drastic decline due to environmental changes, habitat destruction, and illegal collection. The ultimate goals of conservation are to ensure the continuous survival of populations and maintain their evolutionary potential by preserving natural levels of genetic diversity. Great efforts should be made to preserve this species' extant populations and their habitats to prevent further population reductions and preserve its overall genetic basis. Collection of this orchid should be banned and robust legal protection measures should be enforced through local authorities.

Maintenance of high levels of genetic diversity and significant fine-scale genetic structure among age classes in single-tree populations of the endangered epiphytic orchid Laelia speciosa (Orchidaceae) in central Mexico

“…Genetic Diversity. Previous work with L. speciosa had shown the species to maintain relatively high levels of genetic diversity across its range (Ávila-Díaz & Oyama 2007, Rojas-Méndez et al 2017, and our study reinforces this finding and shows that even at the single tree level, a large proportion of the diversity seen in populations is maintained in individual trees.…”

“…High levels of genetic variation (H o = 0.490 (Tree 1) and 0.480 (Tree 2)) were found in the two single-tree populations of L. speciosa analyzed, a reduction by a factor of 1.46 from a population-wide assessment of diversity (H o = 0.714) using the same microsatellite methods (Rojas-Méndez et al 2017) (Table 1). The similarity of total diversity and the lack of differentiation between the trees as shown through AMOVA, shows that these are representative of the diversity found within the orchid meta-population within the continuous forest of Q. deserticola.…”

“…Mantenimiento de altos niveles de diversidad genética y estructura genética a fina escala entre diferentes categorías de edad en dos poblaciones (árboles) de la orquídea epifita Laelia speciosa (Orchidaceae) en México this goal, extraction must be kept to a minimum and reintroductions should take place from individuals within close proximity (Ávila-Díaz & Oyama 2007, Rojas-Méndez et al 2017. While these studies have provided important information regarding patterns of genetic diversity, they have not specifically addressed L. speciosa's epiphytic habit.…”

“…At the range-wide scale, isozyme studies have shown high levels of genetic diversity (polymorphic loci = 76 %, H o = 0.302) (Cole 2003), accompanied with low levels of genetic differentiation among populations (θ p = 0.040), and the presence of private alleles in specific isolated populations using isozymes (Ávila-Díaz & Oyama 2007). At the regional scale within its central area of distribution, analysis with microsatellites also indicates that L. speciosa maintains high levels of genetic diversity (H o = 0.534 -0.715) (Rojas- Méndez et al 2017). While it is known that genetic diversity determined by microsatellite analysis are highly influenced by the type of repeat present in the markers (Merritt et al 2015) and that cross-species comparisons are more difficult, we can see that L. speciosa maintains population genetic diversity values similar to those found in a variety of other Orchidaceae ranging from the insular epiphytic Vanilla humblotii Rchb.…”

“…(H o = 0.619) (Zhao et al 2017) and the recently reduced in range grassland species Platanthera praeclara Sheviak & M. L. Bowles (H o = 0.566 -0.664) (Ross et al 2013). This high diversity is apparently maintained despite being subjected to high rates of direct exploitation and fragmentation of its habitat (Rojas-Méndez et al 2017). The presence of inbreeding and evidence indicating recent bottlenecks in selected populations does suggest that habitat fragmentation is having a negative effect on population genetic diversity and structure and that more extensive conservation measures should be implemented.…”