Habitat fragmentation threatens wild populations of Carica papaya (Caricaceae) in a lowland rainforest

Abstract

• Premise of the study: Wild populations of domesticated species constitute a genetic reservoir and are fundamental to the evolutionary potential of species. Wild papaya (Carica papaya) is a rare, short-lived, gap-colonizing, dioecious tree that persists in the forest by continuous dispersal. Theoretically, these life-history characteristics render wild papaya highly susceptible to habitat fragmentation, with anticipated negative effects on its gene pool. Further, species dioecy may cause founder effects to generate local biases in sex ratio, decreasing effective population size.• Methods: We contrasted the genetic diversity and structure of C. papaya between wild populations from rainforest fragments and continuous forest at Los Tuxtlas, Mexico. We evaluated recent migration rates among populations as well as landscape resistance to gene flow. Finally, we calculated the sex ratio of the populations in both habitats.• Key results: Populations of wild papaya in rainforest fragments showed lower genetic diversity and higher population differentiation than populations in continuous rainforest. Estimates of recent migration rates showed a higher percentage of migrants moving from the continuous forest to the forest fragments than in the opposite direction. Agricultural land and cattle pasture were found to be the most resistant matrices to gene flow. Finally, biased sex ratios were seen to affect the effective population size in both habitats.• Conclusions: The mating system, rarity, and short life cycle of C. papaya are exacerbating the effects of rainforest fragmentation on its genetic diversity, threatening the persistence of its natural populations in the proposed place of origin as well as its genetic reservoir.

Domestication and Genetics of Papaya: A Review

“…Three sex types of papaya are known: female, male, and hermaphrodite trees. In wild populations, most individuals are diclinous (dioecy), whereas cultivated papayas are dioecious or hermaphrodites (Carvalho and Renner, 2012;Chávez-Pesqueira et al, 2014). Cultivars can inbred, resulting in stable characteristics across generations (Manshardt, 1992).…”

“…In mature forests, papaya plants mainly die due to shading by other trees that "close" the canopy gaps by lateral growth. Because of its nomadic nature, wild papaya represents a key element in the regeneration dynamic of tropical and sub-tropical forests along its natural distribution (Chávez-Pesqueira et al, 2014).…”

“…These phenotypes suggest introgression due to occasional mating between population types (Chávez-Pesqueira et al, 2014). Since wild C. papaya represents the genetic reservoir of the species (Chávez-Pesqueira and Núñez-Farfán, 2016), exhaustive efforts should be made to know and preserve this important species in its wild form.…”

Resistencia de Vasconcellea cauliflora al Virus de la mancha anular de la papaya-potyvirus (PRSV-P) y su introgresión en Carica papaya

“…En África tropical se encuentran dos especies del género Cylicomorpha, en América Central se encuentran los géneros endé-micos Horovitzia y Jarilla, además de Jacaratia y Vasconcellea que se encuentran en América del Sur (Antunes y Renner, 2014). La especie Carica papaya silvestre se encuentra extendida en bosques tropicales que van de México hasta Costa Rica (Chávez-Pesqueira et al, 2014). La versión hermafrodita de C. papaya cultivada es producto de la domesticación por grupos étnicos de México, presumiblemente los mayas (VanBuren et al, 2015).…”

“…Two species of the Cylicomorpha genus are in tropical Africa, while the endemic Horovitzia and Jarilla genera prevail in Central America, and Jacaratia and Vasconcellea, in South America (Antunes and Renner, 2014). Carica papaya wild species are widely distributed in tropical forests from Mexico up to Costa Rica (Chávez-Pesqueira et al, 2014). The hermaphrodite version of C. papaya currently sown is the result of domestication by Mexican ethnic groups, presumably the Mayas (VanBuren et al, 2015).…”