Abstract
Recent studies have reported incipient morphological caste dimorphism in the Van der Vecht organ size of some temperate Polistes paper wasps. Whether species other than the temperate ones show a similar pattern remains elusive. Here, we have studied some Neotropical Polistes species. By comparing females collected through the year, we showed caste related differences in the size of the Van der Vecht organ in P. ferreri (body size corrected Van der Vech organ size of queens = 0.45 ± 0.06, workers = 0.38 ± 0.07 mm2, p = 0.0021), P. versicolor (body size corrected Van der Vech organ size of queens = 0.54 ± 0.11, workers = 0.46 ± 0.09 mm2, p = 0.010), but not P. simillimus (body size corrected Van der Vech organ size of queens = 0.52 ± 0.05, workers = 0.49 ± 0.06 mm2, p = 0.238). Therefore, it seems that queens and workers of some Neotropical Polistes have diverged in their ontogenic trajectory of the Van der Vecht organ size, providing clear evidence for incipient morphological caste dimorphism. As Polistes are distributed mostly in the tropics, we propose that physical caste differences may be widespread in the genus. Also, we highlight that morphological divergence in the queen–worker phenotypes may have started through differential selection of body structures, like the Van der Vecht organ.
Highlights
On observing a typical colony full of females of primitively eusocial Hymenoptera, such as ponerine ants, halictid bees, stenogastrine wasps and Polistes paper wasps, one can comprehend that all colony members are morphologically similar
It means that the effect of the overall body size on the Van der Vecht organ size is different in queens and workers, providing evidence for caste-dependent dimorphism in P. ferreri Van der Vecht organ size
We found no evidence for caste-dependent dimorphism in P. simillimus Van der Vecht organ size
Summary
On observing a typical colony full of females of primitively eusocial Hymenoptera, such as ponerine ants, halictid bees, stenogastrine wasps and Polistes paper wasps, one can comprehend that all colony members are morphologically similar. If each individual receives a unique combination of paint on the thorax [1], it is possible for an observer to follow the behavior of each colony member. Caste Differences in Polistes Van der Vecht Organ individuals are less aggressive, forage at higher rates and lay no or only a few eggs, like Polistes wasps [2, 3]. These two behavioral groups constitute examples of castes, broadly defined as subgroups of colony members, genetically, but not physiologically or anatomically homogeneous, that specialize in particular tasks for prolonged periods of time [4]. In colonies of primitively eusocial insects the queen–worker morphology greatly overlaps, meaning that there is a lack of morphological castes, in colonies of highly eusocial insects there is little or no overlap between the queen–worker morphology, so that physical castes do exists [5, 6]
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