Genetic diversity in restored areas of the Atlantic Forest surprises researchers

Parameters found are similar to those of forest remnants. Analysis focused on four species of plants with phytotherapeutic potential.

By Karina Toledo

Agência FAPESP – Researchers at the São Paulo Agency for Agrobusiness Technology (APTA) were surprised to find no significant differences in most parameters when they compared the genetic diversity of plants in three forest remnants of the Atlantic Forest with that of two areas in the process of restoration, all in inland São Paulo State.

Only in terms of allelic richness (the number of different alleles for a single region of the genome) and private allelic richness (exclusive to a particular population) were the percentages found in the native forest areas larger than those in the reforested areas.

The analysis, which was conducted with support from FAPESP, focused on four species with phytotherapeutic potential: ararib (Centrolobium tomentuosum, an anti-inflammatory and antileishmanial), cabreuva (Myroxylon peruiferum, antibiotic and analgesic), guacatonga (Casearia sylvestris, anticarcinogen) and pau-jacaré (Piptadenia gonoacantha, antioxidant).

The data were presented by researcher Maria Imaculada Zucchi of APTA during the 7th Assessment Meeting of the BIOTA-FAPESP Program, held in São Paulo on August 7, 2014.

“The genetic diversity is directly related to the longevity of a population and its capacity to evolve in response to environmental changes. However, for some decades now, restoration projects have been implemented with high interspecies diversity [many different species] but little or no attention to intraspecies diversity [seeds originating from a few matrices of each species]. This is why the outcome of the study surprised us,” Zucchi said.

The use of seeds collected from a small number of matrices, explained the researcher, may limit the genetic basis in the areas of restored forest, resulting in a population that consists of plants that are related to each other.

“Initially, no problem is observed. However, when they reach the phase of reproduction, there will be a large amount of inbreeding, causing endogamy and potentially increasing the frequency of deleterious or lethal alleles in these populations, leading to a decreased population or a complete decline,” Zucchi explained.

Another consequence of the use of plants with a restricted genetic basis in reforested areas is the so-called “founder effect,” the establishment of a new population formed by a small number of genotypes.

To determine whether reforested areas of São Paulo have suffered from this phenomenon, scientists from APTA and students from the graduate program in genetics and molecular biology of the Institute of Biology (IB) at the University of Campinas (Unicamp) collected samples of the four phytotherapeutic species in the region of Cosmópolis, which has been in the process of restoration for 54 years, and in Iracemápolis, which has been in restoration for 24 years.

Collections were also made in the forest remnants of the Caetetus Ecological Unit, associated with the Forestry Institute of the state of São Paulo and situated in the Gália region; at the Tietê Research and Development Unit (UPD-Tietê) of APTA; and in the Mata de Santa Genebra Area of Special Ecological Interest (ARIE), in the municipality of Campinas.

In all, 414 samples of ararib, 182 of cabreuva, 546 of guacatonga and 394 of pau-jacaré were collected. Of this total, 20 seed-producing matrices from each species were collected for the purpose of studying the breeding rate. The next step was to extract the DNA from the samples to determine the genotype – using a method similar to that used in human paternity tests – and calculate the frequencies of the different alleles found.

According to Zucchi, there was no significant difference between the areas studied in terms of most of the parameters of genetic diversity, which runs counter to various population factors such as the number of heterozygote individuals found.

One slight difference was found in the percentages of allelic richness. In the case of the guacatonga, the numbers were 64% in the native areas and 36% in the restored areas. For cabreuva, the percentages were 54% and 46%, respectively. For ararib, they were 52% and 48%, and for pau-jacaré, they were 56% and 44%.

The researchers also compared the values of the so-called private alleles – those that are exclusive to the population studied. In this case, it became clear that there was a discrepancy between the areas because, for the guacatonga, the percentages were 92% in the forest remnants compared to 8% in the restored areas. In the case of cabreuva, the percentages were 74% and 26%, respectively. For ararib, they were 70% and 30%, and for pau-jacaré, they were 68% and 32%.

One possible explanation for the very slight variation in the parameters of genetic diversity may be the occurrence of gene flow from forest remnant areas to the nearby reforested areas – a process that Zucchi says became clear from the data on cabreuva.

“The young individuals from the restored areas had alleles that were not shared with the adult individuals of the same area but were similar to the alleles found in adults from the nearby forest remnants, suggesting the occurrence of gene flow from native to restored areas,” the researcher said.

The study of the rate of breeding indicated that the species under study present a mixed system of breeding. They can self-fertilize (autogamy) as well as breed with other individuals from the same species (allogamy). The exception was the ararib, which showed a tendency toward allogamy.

“In developing a conservation project, one of the first things to be studied is the breeding rate, to understand how the species reproduce. This is important for calculating how many different matrices will be used in a particular area to ensure the necessary genetic diversity,” Zucchi explained.

Population genomics

In recent decades, according to Zucchi, forest restoration has ceased to be a simple matter of planting trees to cover deforested areas. Instead, it has become a science that seeks to rebuild complex ecological interactions in plant communities degraded by human activity.

In an article published in the Journal of Biotechnology and Biodiversity, researchers at APTA and the Luiz de Queiroz College of Agriculture (Esalq) at the University of São Paulo (USP) discuss how notions of population genetics can contribute to making restoration policies even more effective.

“Indicators of a population’s genetic diversity are important in association with other conservation tools so that we can introduce reforested areas with the minimum levels of allelic richness and genetic diversity to help connect them to the remaining native forests, restoring the ecological processes and ensuring functional ecosystems that are biologically viable over time,” Zucchi said.