Reduced resistance of invasive varieties of the alien tree Sapium sebiferum to a generalist herbivore

Abstract

Invasive plants are often larger in their introduced range compared to their native range. This may reflect an evolved reduction in defense and increase in growth in response to low herbivory in their introduced range. Key elements of this scenario include genetic differences in defense and growth yet uniformly low rates of herbivory in the field that dissociate defense and herbivore damage for alien species. We conducted a laboratory experiment with Melanoplus angustipennis grasshoppers and Chinese Tallow Tree seedlings ( Sapium sebiferum) from its native range (China) and its introduced range (Texas, USA) where it is invasive. We caged grasshoppers with pairs of Sapium seedlings from the same continent or different continents. The amounts of leaf area removed from Texas and China seedlings, and their height growth rates, were indistinguishable when both seedlings in the pair were from the same continent. However, when grasshoppers had a choice between seedlings from different continents, they removed more Texas Sapium foliage than China Sapium foliage and height growth rates were higher for China Sapium seedlings compared to Texas seedlings. Grasshopper growth rates increased with greater Sapium foliage consumption. In a common garden in Texas, Sapium seedlings from Texas grew 40% faster than those from China. Chewing insect herbivores removed little Sapium foliage in the field experiment. Although grasshoppers preferred to feed on Texas Sapium when offered a choice in the laboratory, extremely low herbivory levels in the field may have allowed the Texas seedlings to outperform the China seedlings in the common garden. These results demonstrate post-invasion genetic differences in herbivore resistance and growth of an invasive plant species together with a decoupling of defense and herbivore choice in the introduced range.

Variation of pyrrolizidine alkaloids in Senecio vulgaris plants from native and invasive ranges

“…For instance, invasive genotypes of Sapium sebiferum evolved to reduced their defense and resistant ability, but the compensative mechanisms that contribute to their invasion success were more tolerant and outperformed than the native genotypes under higher levels attack (Siemann & Rogers 2003;Rogers & Siemann 2004;Zou et al, 2008). This study found evidences support that the qualitative defense slightly reduced in the invasive S. vulgaris plants; while our previous study demonstrated that the invasive S. vulgaris plants grew and reproduced better than those from the native range (unpublished data).…”

Higher resistance to herbivory in introduced compared to native populations of a seaweed

“…In some of the studied species, populations from the new range were found to be less resistant to herbivory than those from the native range (Blossey and Nötzold 1995;Willis et al 1999;Siemann and Rogers 2003;Wolfe et al 2004). This has been put forward as support for the enemy release hypothesis; the NIS is released from specialist herbivores and can decrease resource allocation to defence and thereby increase its competitive ability.…”

Seedbank Potential of Chinese Tallow Tree (Triadica sebifera) in a Texas Bottomland Hardwood Forest

“…They determined that grasshoppers consumed similar amounts of both genotypes, suggesting that Chinese tallow may have been a palatable host plant since its introduction, but that fixed behavioral avoidance by generalist herbivores may contribute to Chinese tallow's low herbivore load in its introduced range (Lankau et al, 2004). In a similar experiment, Siemann and Rogers (2003a) (Siemann and Rogers, 2003b).…”