Livestock can affect the evolutionary potential of native plant species in Monte Desert

JAUME, DAIANA; PELLIZA, YAMILA IVÓN; TADEY MARIANA; SOUTO CINTIA

Congreso; The I Meeting of Systematics, Biogeography, and Evolution (SBE); 2021

Understanding how anthropogenic disturbances affect genetic, ecological and evolutionary processes aids the development of sustainable management and conservation strategies, particularly in drylands threatened by desertification. Introduction of domestic livestock in natural areas of arid environments affects the dynamics and stability of plant communities with unpredictable evolutionary consequences. We hypothesize that livestock grazing exert selective pressures, negatively affecting genetic diversity and fitness of consumed plants, and also of their offspring. We predict lower genetic diversity (heterozygosity and allelic diversity) and fitness (reproductive success and seedling vigor) in rangelands with high stocking levels(HSL) compared to those with low stocking level (LSL), in both parental and offspring generations. We collected foliage and seeds of Atriplex lampa, a dominant consumed bush of the Patagonian Monte Desert, from two rangelands with HSL and LSL, measuring fitness (height and diameter, % reproductive branches, seed weight and viable seed proportion). We sowed seeds under common garden conditions and evaluated offspring vigor as height and branch number. We calculated standard population genetic parameters using microsatellite markers. As expected, we detected significantly lower genetic diversity in rangelands with HSL (He = 0.354 and Ad = 0.251) compared to those with LSL (He = 0.441 and Ad = 0.291) (all p < 0.05). Fitness parameters and vigor were negatively associated with browsing (all p < 0.05). Regarding reproductive success, viable seed proportion was lower at LSL (77.2%) than at HSL (85.8%), p = 0.017. Although, HSL seeds weight (1.200 g) was lower than in LSL (1.300 mg), p = 0.06. Furthermore, allelic diversity was associated with seed weight (β = 0.173), and offspring branch number (β = 10.977, p ≤ 0.06). Parental individual heterozygosity was positively associated with plant cover (p =0.01), suggesting natural revegetation may be compromised. Endogamy was high in both rangelands and generations (Fis ≥ 0.326), while only parental generation at HSL exhibited a significant excess of heterozygosity, indicating a recent genetic bottleneck. Our results show that domestic livestock cause genetic diversity loss between generations in a highly consumed desert shrub. With parental and offspring generations showing high levels of inbreeding. Also, livestock reduced plant fitness and vigor, even with unexpectedly viable seed proportions. Unmanaged grazing seriously affects dryland vegetation sustainability, creating a disturbance that threatens plant evolutionary potential. Highlighting the importance of considering preserving genetic diversity across generations not only to protect the evolutionarypotential of the species but also to protect the ecological services of the system by the development of sustainable management and conservation strategies.