Low genetic variation in tolerance to defoliation in a long-lived tropical understorey palm

Abstract

20Defoliation is a ubiquitous stressor that can strongly limit plant performance. Tolerance to defoliation 21 is often associated with compensatory growth. Genetic variation in tolerance and compensatory growth 22 responses, in turn, play an important role in the evolutionary adaptation of plants to changing disturbance 23 regimes but this issue has been poorly investigated for long-lived woody species. We quantified genetic 24 variation in plant growth and growth parameters, tolerance to defoliation and compensatory responses 25 to defoliation for a population of the understorey palm Chamaedorea elegans. In addition, we evaluated 26 genetic correlations between growth and tolerance to defoliation. 27 We performed a greenhouse experiment with 731 seedlings from 47 families with twelve or more 28 individuals of C. elegans. Seeds were collected in southeast Mexico within a 0.7 ha natural forest area. 29A two-third defoliation treatment (repeated every two months) was applied to half of the individuals to 30 simulate leaf loss. Compensatory responses in specific leaf area, biomass allocation to leaves and growth 31 per unit leaf area were quantified. 32 We found that growth rate was highly heritable and that plants compensated strongly for leaf loss. 33However, genetic variation in tolerance, compensation, and the individual compensatory responses was 34 low. We found strong correlations between family mean growth rates in control and defoliation 35 treatments. We did not find indications for growth-tolerance trade-offs: genetic correlation between 36 tolerance and growth rate were not significant. 37The low genetic variation in tolerance and compensatory responses observed here suggests a low 38 potential for evolutionary adaptation to changes in damage or herbivory, but high ability to adapt to 39 changes in environment that require different growth rates. The strong correlations between family mean 40 growth rates in control and defoliation treatments suggest that performance differences among families 41 are also maintained under stress of disturbance. 42 3 43 Introduction 44Defoliation due to herbivory, pathogens, physical damage or harvesting is an ubiquitous 45 stressor that can strongly limit individual plant performance (i.e. growth, reproduction and 46 survival) as it entails a reduction in photosynthesis and resources, and thus in future growth. 47Performance reductions due to defoliation are often proportionately smaller than expected 48 based on the fraction of leaf area that is being removed [1, 2] and in some cases plants even 49 increase their performance under defoliation [3, 4]. In that sense plants can be tolerant to 50 defoliation, and this tolerance is often associated with compensatory growth, a mechanism by 51 which negative effects of leaf loss are mitigated [5]. There are three types of compensatory 52 growth responses: plants can compensate for growth by allocating more new assimilates to 53 leaves, by allocating new assimilates more efficiently to leaf area (i.e. by increasing ...