An understanding of the mechanisms and functions of animal migratory behaviour may provide insights into its evolution. Furthermore, knowledge about migration may be important for conservation of rare species and may help to manage species in a rapidly changing world. Upstream migration is common in riverine animals, but little is known about proximate cues and functions of the upstream migration in aquatic macroinvertebrates. In Ubon Ratchathani, Thailand, locals have observed a synchronous mass migration of freshwater shrimps on land. This so‐called ‘parading behaviour' occurs annually during the rainy season and has become a large ecotourism event. Yet, we know little about the natural history, proximate causation and function of this extraordinary behaviour. Here we describe the natural history of parading behaviour and report the results from a series of experiments and observations to address its mechanisms and functions. Parading behaviour is not associated with breeding and spawning; rather, shrimps leave the water to escape strong currents. Conditions promoting shrimps to leave the water include low light, high water velocity and low air temperature. In addition, there is variation explained the specific location. River topology that creates hydrological variability and turbulence plays a role in triggering the shrimps to move out of water. Furthermore, turbidity and water chemistry were associated with shrimp activity. Finally, our results support that parading behaviour in freshwater shrimps is a mass movement upstream due to hydrological displacement. This study highlights the mechanisms that stimulate parading behaviour; a common activity in Macrobrachium and other decapod crustaceans.
The Sarcastic Fringehead (Neoclinus blanchardi, Teleostei) exhibits an extreme version of a common aggressive display, the "gaping display," in which an open mouth is presented toward an opponent. Males of this species have extremely long jaws that extend posteriorly well past the posterior margin of the head and are flared laterally during the gaping display. In this study, we explored morphological traits related to this extraordinary display in this and related species of blennies. Morphological modifications include enlargement of the buccopalatal membrane, elongation of the maxilla via an uncalcified posterior extension, and evolution of a novel hinge between the anterior maxilla and lacrimal bones permitting lateral movement of the upper jaw. Geometric morphometry using the truss network system, thin-plate spline, and PCA of three closely related species of Neoclinus indicate that the elongate maxilla of N. blanchardi most likely evolved via acceleration (faster growth compared to outgroups) and hypermorphosis (continued growth to a larger body size), both forms of peramorphic heterochrony. Coloration and fluorescence of the buccopalatal membrane may also serve to amplify the extraordinary gaping display of the Sarcastic Fringehead.
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