The effects of fragmentation on the genetic structure of Theobroma speciosum (Malvaceae) populations

Abstract

Native Theobroma species, such as cacauhy, are losing their habitat due to the intense forest fragmentation in the Amazon region, and preserving their genetic diversity has been the focus of many conservation programs. The aim of the present study is to assess whether fragmentation and habitat reduction affect its genetic structure and lead to genetic diversity losses in natural Theobroma speciosum populations. The study was conducted in two Mato Grosso State (Brazil) locations: Apiacás and Alta Floresta counties. Juruena National Park (JNP) in Apiacás County holds a natural T. speciosum population that has not suffered anthropic influences. A population composed of individuals from three anthropized urban forest parks (UF) in Alta Floresta County was analyzed for comparison. The leaves of 75 T. speciosum individuals distributed in the urban forest fragments and of 100 individuals found in the Juruena National Park were sampled. All nine microsatellite loci showed high polymorphism levels between categories (adults and sub-adults), in both populations. The sub-adult individuals of the fragmented area had a higher value (0.71), and the preserved population, the same value (0.69). The analysis of molecular variance showed 83 % genetic diversity within categories; 16 %, between populations; and only 1 %, between categories. Although the effects were small, a persistent fragmentation process can increase inbreeding and facilitate genetic drift, leading T. speciosum populations to inbreeding depression and loss of diversity. Rev. Biol. Trop. 66(1): 218-226. Epub 2018 March 01.Key words: genetic variability, cacauhy, inbreeding, Amazon, anthropic influence, microsatellite.The Amazon is an extraordinary supplier of natural resources to the Brazilian and world populations. The sustainable use of these resources and the lack of biological knowledge about most of the Amazonian flora species are challenges for future generations (Silva et al., 2015).Theobroma speciosum Willd. ex Spreng. (cacauhy) is native to the Amazonian region and it is distributed in primary forests of unflooded lands. This species, although little known, is important because it represents a possible source of resistance among most of the economically relevant species belonging to genus Theobroma (Silva et al., 2015).Native Theobroma species, such as cacauhy, are losing their habitat due to the intense forest fragmentation in the Amazon, and thus preserving the genetic diversity has been the main goal of most conservation programs focused on preserving the gene of interest and on allowing species variability maintenance at genetic level (Bekessy et al., 2002).Forest fragmentation decreases the number of individuals in a given population and, consequently, favors genetic variation losses. Genetic drift is the measured gene frequency of these individuals. In the short term, apart from the gene frequency of the original population, including the allele losses, genetic drift may occur in this small population. It is likely to have increased inbre...

Evaluation and potential use of native forest species in the recovery of a legal reserve in the Western Amazon

“…Other species with a lower importance value found in the composition of the sampled plots, have been described in the literature as of potential use in production systems, one example being Theobroma speciosum, with an IV of 1.82%. The species is described as native to the Amazon (DARDENGO et al, 2018) and its fruit is used as food by indigenous peoples (SANTOS JÚNIOR et al, 2017). It has been employed in the composition of agroforestry systems (LEÃO et al, 2017) and its seed used in the commercial production of cocoa (PAIVA et al 2011).…”

“…Cita-se, exemplamente, Theobroma speciosum, que apresentou VI de 1,82%. A espécie é descrita como nativa da Amazônia (DARDENGO et al, 2018), seus frutos são utilizados como alimento pelos povos indígenas (SANTOS JÚNIOR et al, 2017). Tem sido utilizada na composição de agroflorestas (LEÃO et al, 2017) e no aproveitamento das sementes para a produção de cacau comercial (PAIVA et al 2011).…”

GENETIC DIVERSITY OF Hymenaea courbaril L. IN THE MATO GROSSO AMAZON: IMPLICATIONS FOR CONSERVATION

“…In the north region of Mato Grosso, the genetic diversity of native species like Theobroma speciosum Willd. ex Spreng has been negatively affected by habitat fragmentation (DARDENGO et al, 2018).…”

Microsatellites are important for forest genetic resources conservation in Brazilian biomes

“…In studying the effects of fragmentation on the genetic structure of Theobroma speciosum populations, Dardengo et al (2018) found that most of the genetic diversity was distributed within groups (83 %), which means that no significant effect of fragmentation was observed. However, given the small number of reproductive individuals in the population, the authors warned that the process of continuous fragmentation might increase inbreeding and favor genetic drift, leading populations to inbreeding depression and diversity loss.…”