Population genetic structure of two columnar cacti with a patchy distribution in eastern Brazil

Area of Science:

• Botany
• Population Genetics
• Conservation Biology

Background:

• Cacti species, including Praecereus euchlorus and Pilosocereus machrisii, exhibit patchy geographic distributions in eastern Brazil's xeric habitats.
• Understanding the genetic structure of these species is crucial for inferring historical processes shaping their distribution.

Purpose of the Study:

• To investigate the genetic variability and population genetic structure of Praecereus euchlorus and Pilosocereus machrisii.
• To explore the genetic diversity of Pilosocereus vilaboensis, Pilosocereus aureispinus, and Facheiroa squamosa.
• To elucidate the historical mechanisms behind the patchy distribution of P. euchlorus and P. machrisii.

Main Methods:

• Analysis of genetic variability and population genetic structure using population genetics markers.
• Calculation of genetic diversity indices (e.g., P, A(p), H(e)).
• Assessment of inbreeding (F(IS)) and genetic differentiation (F(ST)) among populations.
• Estimation of gene flow (N(m)) and analysis of isolation by distance.

Main Results:

• All studied species exhibited high genetic variability at the populational level, contrary to expectations based on small population sizes.
• Substantial inbreeding was detected within populations (F(IS) values ranging from 0.370 to 0.623).
• P. euchlorus and P. machrisii showed high genetic differentiation (F(ST) = 0.484 and 0.281, respectively) with no evidence of isolation by distance, indicating low gene flow (N(m) < 1).
• Genetic distance between P. machrisii and P. vilaboensis suggests potential local speciation or introgression.

Conclusions:

• Historical fragmentation is the primary mechanism driving the patchy distribution of P. euchlorus and P. machrisii.
• The findings challenge assumptions about low genetic variability in small, fragmented populations.
• Genetic data indicate potential taxonomic issues within the Pilosocereus genus, possibly involving speciation or introgression.