Background and Aims:

Several studies have emphasized the important role of howler monkeys (Alouatta palliata mexicana) in seed dispersal and, as a result, in the regeneration of fleshy-fruited plant populations in tropical forests. However, there is little empirical evidence regarding the possible mechanisms that would allow howler monkeys to promote seed germination of many plant species, including seed coat scarification. In this study, we evaluated whether endocarps of Spondias mombin (Anacardiaceae), an important species in howler monkey diet, could be scarified by passage through the digestive tract of these primates.

Methods:

We collected endocarps from howler monkey feces as well as ripe fruits fallen on the ground, in the region of Los Tuxtlas, Catemaco municipality, Veracruz, Mexico. By analyzing endocarp transverse sections using a scanning electron microscope, we measured the thickness of the outer layer and tested differences between both types of samples (i.e., fruit endocarps and endocarps that had passed through the digestive tract).

Key results:

We observed that the outer layer thickness of endocarps in fruits was greater ($\tilde{\mathrm{X}}$=47.05±9.69 µm) than that of endocarps found in feces ($\tilde{\mathrm{X}}$=1.51±3.60 µm) (W=0.48, p<0.001).

Conclusions:

Our results highlight that consumption of S. mombin endocarps by A. p. mexicana may have a scarification effect on the tissues that constitute the outer layer. This supports the hypothesis of the role of frugivores, such as howler monkeys, in reducing the seed coat and thus increasing germination ability; therefore, being key organisms in regeneration dynamics of tropical forests.

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