| Zusammenfassung: | The fundamental ethological display of Scarabaeinae (Insecta: Coleoptera: Scarabaeidae) is the relocalization of foo: relocalization for the adult's use or for nesting. Relocalization can be either vertical or horizontal. The basic ethological and morphological division of the Scarabaeinae into burrowers and rollers is determined by whether one or the other is done. The rollers relocate horizontally by forming a ball at the food source (dung or carrion), rolling it for a certain distance and then buring it (or not). When the ball is for the adult's food, the process is carried out by one specimen, male of female; when the ball is for nesting, the process is carried out by a bisexual pair and once the ball has been rolled it is transformed by the female into a brood-ball. Both processes are characteristic and unique- in the whole animal kingdom- of the Scarabaeini, the rolling beetles. This paper is dedicates to the analysis of the origin and evolution of the processes involved in ball formation and rolling and the relationship between the two. In order to do this all the known cases where one or the other of these fundamental behavioral displays are lacking were analyzed. The analysis starts with the reexamination of all the exceptions to rolling and ball formation pointed out in the first synthesis on the biology of Scarabaeinae (Halffter and Matthews, 1966). The Australian examples observed by Matthews (1974) are also examined as well as observations published subsequently. The second part of this paper describes the behavior of Canthon obliquus, an endemic species from the southern part of Baja California, whose biology was completely unknown up to now. This beetle does not make ball for food, and it does not roll therm on the surface, although it can occasionally separate a small fragment of dung and relocate it holding it with the tarsii of the posterior legs, while it walks on the anterior and middle ones. For nesting it makes balls which it inmediately burys under the dung pad. The third part of the paper is a discussion on the processes of ball formation and rolling and their interrelation within the general context of the evolution of feeding and reproductive behavior of Scarabaeinae. The main ideas of the hypothesis (advanced in part by Halffter and Matthews, 1966; Halffter, 1977; Halffter and Edmonds, 1982) are: Scarabaeinae are part of a monophyletic group whose ethological evolution is centered around the ecological problem of the excrement of large vertebrates. A series of important common morphological characteristics (analyzed in detail by Halffter and Edmonds, 1982) reinforce the idea of this monophyletic origin. The tribe Scarabaeini detaches itself early from the common truk, probably before the end of the Mesozoic era, but not before a fundamental gain regarding the nesting of the subfamily has been established: the formation by the mother of an individual and isolated brood-ball. In the most primitive burying Scarabaeinae, the brood-ball is not present. The most evolved forms of burrowers arrive at the brood-ball by following at least three different behavioral sequences. As far as we know, all rollers make a brood-ball in a similar way. The brood-ball is considered fundamental as it guarantees the efficient isolation and protection of the egg, larva and pupa. It is accompanied by the lack of ability to make a pupal cocoon at the end of the larval development and by the acquisition of a perfected mechanism of repair; in a similar manner the maternal activity is perfected through the recoating of the brood-ball by a layer of scil and/or the care of the mother during development. From the analysis carried out in this paper the outstanding fact is that all rollers whose nesting is known make a brood-ball from which we can deduce-until evidence to the contrary is found- that the capacity to execute the complex series of movements necessary to separate the ball is present in the whole tribe, although because of local or regional ecological conditions it may not be used for feeding behavior. We postulate that the capacity to elaborate the ball has evolved simultaneously with the rollling and not independently and after this process as Eric G. Matthews suggests for the Australian forms. In a certain number of cases in which the non-formation of a ball on the surface has been pointed out, subsequent observations have demonstrated that this is possible when the scarab finds itself before excrement which has the adecuate texture and size. There are still some species in which ball formation has never been observed in the feeding processes. We consider that in all cases where ball formation has never been observed in the feeding processes. We consider that in all cases where ball formation is not present or only manifests itself occasionally, it is because of a derived behavior due to special ecological conditions, such as the lack (during a long evolutionary period- Australia- or because of local or regional conditions) of an abundant and adequate excrement and the presence, on the other hand, of pellets. What really stands out is the fact that as has been demostrated in many of these species, the capacity to make a ball has been preserved when the adequate material and conditions are present and that the, up to now universal, permanence of the brood-ball formation is a fundamental part of nesting. The fact that nesting behavior is more conservative compared with feeding behavior is made obvious. In this way, as recent papers on burying species of the subfamily are begining to point out, the ecological pliability of the Scarabaeinae's behavior becomes evident. The outstanding aspect of the Scarabaeini's behavior is the importance of bisexual cooperation, essential to the rolling process for the future brood-ball. Two roll better and faster than one. A series of morphological experimental discoveries over the last decade point out the enormous importance of chemical communication through pheromones.
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