Allometric shape change of the lower pharyngeal jaw correlates with a dietary shift to piscivory in a cichlid fish

Abstract

The morphological versatility of the pharyngeal jaw of cichlid fishes is assumed to represent a key factor facilitating their unparalleled trophic diversification and explosive radiation. It is generally believed that the functional design of an organism relates to its ecology, and thus, specializations to different diets are typically associated with distinct morphological designs, especially manifested in the cichlids' pharyngeal jaw apparatus. Thereby, the lower pharyngeal jaw (LPJ) incorporates some of the most predictive features for distinct diet-related morphotypes. Thus, considering that piscivorous cichlids experience an ontogenetic dietary shift from typically various kinds of invertebrates to fish, concomitant morphological changes in the LPJ are expected. Using Lepidiolamprologus elongatus, a top predator in the shallow rocky habitat of Lake Tanganyika, as model, and applying geometric and traditional morphometric techniques, we demonstrate an allometric change in ontogenetic LPJ shape development coinciding with the completion of the dietary shift toward piscivory. The piscivorous LPJ morphotype is initiated in juvenile fish by increasing elongation and narrowing of the LPJ and--when the fish reach a size of 80-90 mm standard length--further refined by the elongation of the posterior muscular processes, which serve as insertion for the fourth musculus levator externus. The enlarged muscular processes of the fully mature piscivorous morphotype provide for the construction of a powerful lever system, which allows the large individuals to process large prey fish and rely on exclusive piscivory.

Thermal Resilience of Feeding Kinematics May Contribute to the Spread of Invasive Fishes in Light of Climate Change

“…Perhaps among the traits that enable the invasive Mayan cichlid to spread northward in Florida is its tolerance to extreme variations in salinity [55,56,57,58] and temperature [56,58]. In addition, the invasive Mayan cichlid has a generalist diet, feeding on detritus, plants, invertebrates and fish [59,60,61,62]. Its feeding apparatus includes an oral-jaw mechanism for prey capture and a well-developed pharyngeal-jaw apparatus for prey-processing [63].…”

The Utility of Geometric Morphometrics to Elucidate Pathways of Cichlid Fish Evolution

“…They were able to distinguish among those groups, but also revealed trophic morphological variation between species within each trophic guild. Other studies showed that GM is not only applicable to quantify tooth shape in the oral jaw [53, 60] but is also an adequate method to investigate differences in pharyngeal jaws [45, 61, 62]. These studies confirmed that this structure is a highly adaptive morphological feature which is optimized for processing several different types of food in cichlid fishes.…”

“…Differences in adult shape may be due to differences arising early in development, and not to the difference of shape change during growth. A very recent study [45] described allometric shape change of the lower pharyngeal jaw in a Lake Tanganyika cichlid fish and could correlate those shape changes to a dietary shift in ontogeny of this species. In Figure 3(b), which originated from the work of Hellig et al [45], it becomes clear that illustration of results is one great advantage of GM.…”

“…Landmarks on (a) cichlid overall body (b) cichlid head [43] (c) a bony element (premaxilla) [44] and (d) the lower pharyngeal jaw [45]. …”

The Effects of Temperature on the Feeding Performance of Invasive Fishes

“…It is believed to have been introduced in the Everglades National Park, Florida (USA) in 1983 [52].Its range of invasive distribution in Florida extends as far north as Merritt Island on the east coast and Tampa area on the west coast [36,53].The invasive Mayan cichlid has a generalist diet compared to the piscivorous diet of the invasive lionfish; it feeds on detritus, plants, invertebrates and fish [52,[54][55][56][57].Just like the generalized species in the family Cichlidae, the Mayan cichlid has an oral-jaw prey-capture mechanism and a well-developed pharyngeal-jaw apparatus for prey-processing that is characteristic of the family [58].…”