A Male Poecillid's Sexually Dimorphic Body Plan, Behavior, and Nervous System (original) (raw)

A Novel Body Plan Alters Diversification of Body Shape and Genitalia in Live-Bearing Fish

Frontiers in Ecology and Evolution, 2021

Major evolutionary innovations can greatly influence subsequent evolution. While many major transitions occurred in the deep past, male live-bearing fishes (family Poeciliidae) more recently evolved a novel body plan. This group possesses a three-region axial skeleton, with one region—the ano-urogenital region—representing a unique body region accommodating male genitalic structures (gonopodial complex). Here we evaluate several hypotheses for the evolution of diversity in this region and examine its role in the evolution of male body shape. Examining Gambusia fishes, we tested a priori predictions for (1) joint influence of gonopodial-complex traits on mating performance, (2) correlated evolution of gonopodial-complex traits at macro- and microevolutionary scales, and (3) predator-driven evolution of gonopodial-complex traits in a post-Pleistocene radiation of Bahamas mosquitofish. We found the length of the sperm-transfer organ (gonopodium) and its placement along the body (gonopo...

Courtship, copulation, and genital mechanics in Physocyclus globosus (Araneae, Pholcidae)

Canadian Journal of Zoology, 1997

The pholcid spider Physocyclus globosus (Taczanowski, 1873) was observed and videotaped courting and copulating, and genital mechanics and movements were analyzed by serial sectioning of freeze-fixed pairs. Just prior to copulation, the chelicerae of the male engage an apophysis on the female's epigynum. During copulation the male vibrates his abdomen rhythmically and makes repeated, relatively stereotyped twisting and flexing movements with his pedipalps, which are inserted simultaneously but asymmetrically in the female. The palps squeeze the female in the area of her epigyneal plate. Copulation with non-virgin females results in the extrusion of a mass of sperm from the female's genitalia during copulation or up to several minutes after it ends; no such masses result from copulations with virgin females. Sperm extrusion was not associated consistently with precedence of sperm from either the first or the second male. It is argued that the palpal movements, and perhaps most rhythmic genitalic movements, in spiders may best be interpreted as a result of sexual selection by means of cryptic female choice, and probably function to provide females with additional information about the male. Pholcids in general, and some genera in particular (including Physocyclus), may be unusual in that the vigour of males may play a significant role during copulatory courtship, as their palps have massive muscles that are only used during copulation.

Sexual dimorphism in amphipods: the role of male posterior gnathopods revealed in Gammarus pulex

Behavioral Ecology and Sociobiology, 2005

In the mate-guarding amphipod, Gammarus pulex, the enlarged male posterior gnathopods have been variously suggested to function to grasp and subdue the female, to be used as weapons in fights between males, to signal to the female the male presence and stimulate moult accelaration, egg development or egg extrusion. These hypotheses were tested in a series of experiments, the results of which reveal an unexpected function. Ablation of the posterior gnathopods of males showed that they were neither necessary for, nor advantageous in, establishment and/or maintenance of precopula mate guarding, with or without competition with intact males. Furthermore, these appendages do not function to advance female moult, or stimulate egg development or extrusion. However, only males with intact posterior gnathopods were able to copulate. We also show that females require a full copulation of several bouts to extrude eggs. We conclude that the function of the posterior gnathopods is to facilitate copulation and suggest future studies focus on the selective pressures acting on copulating males.

Functional significance of intramandibular bending in Poeciliid fishes

Environmental Biology of Fishes, 2008

Substrate-feeding teleosts show multiple, independent evolutionary acquisitions of intramandibular bending (bending within the lower jaw)-a behavior that likely enhances performance when feeding on attached or encrusting food items. However, intramandibular bending has only been quantified for marine teleosts. Here, we examine substrate feeding in eight species from the order Cyprinodontiformes and quantify movements produced by the anterior jaws of four target species selected from the family Poeciliidae to represent a variety of trophic strategies. Intramandibular bending, defined here as bending between the dentary and angular-articular bones of the lower jaw, is not present in some poeciliids (i.e. Gambusia affinis), nor is it present in outgroup cyprinodontiforms (i.e. Fundulus rubrifrons). However, intramandibular bending is present in certain poeciliids (i.e. Poecilia sphenops), and can exceed 90°. Such jaw bending enables the production of a gape angle that approaches 120°, which likely allows the fish to maximize contact between the toothed tips of the jaws and the substrate during the bite. Intramandibular bending in poeciliid species is associated with specific trophic shifts: the greater the intramandibular bending in a given species, the more attached algae (periphyton) reported in its diet. This result supports the hypothesis that intramandibular bending enhances performance when feeding on encrusting food items. We predict that additional examples of functional convergence are likely to be documented in freshwater teleosts as more herbivorous species are examined, and we propose that intramandibular bending represents an excellent model system in which to examine the functional processes that underlie convergent evolution.

Unusual kinematics and jaw morphology associated with piscivory in the poeciliid, Belonesox belizanus

Zoology, 2010

Piscivory in fishes is often associated with the evolution of highly elongate jaws that achieve a large mouth opening, or gape. Belonesox belizanus, the pike killifish, has independently evolved this morphology, which is derived from short-jawed poeciliids within the Cyprinodontiformes. Using kinematic analysis of highspeed video footage, we observed a novel aspect of the elongate jaws of Belonesox; the premaxilla rotates dorsally during mouth opening, while the lower jaw rotates ventrally. Anatomical study revealed that this unusual motion is facilitated by the architecture of the premaxillomandibular ligament, prominent within cyprinodontiforms. In Belonesox, it allows force to be transferred from the lower jaw directly to the premaxilla, thereby causing it to rotate dorsally. This dorsal rotation of the premaxilla appears to be assisted by a mediolateral twisting of the maxilla during jaw opening. Twisting maxillae are found in members of the group such as Fundulus, but are lost in Gambusia. Models revealed that elongate jaws partially account for the enlarged gape, but enhanced rotation at the quadrato-mandibular joint was equally important. The large gape is therefore created by: (i) the convergent evolution of elongate jaws; (ii) enhanced jaw rotation, facilitated by loss of a characteristic cyprinodontiform trait, the lip membrane; and (iii) premaxilla rotation in a novel direction, facilitated by the retention and co-option of additional cyprinodontiform traits, the premaxillomandibular ligament and a twisting maxilla.

A novel, sexually selected trait in poeciliid fishes: female preference for mustache-like, rostral filaments in male Poecilia sphenops

Behavioral Ecology and Sociobiology, 2010

Female choice can often drive the elaboration of male traits, leading to the evolution of secondary sexual traits. In the Mexican molly, Poecilia sphenops (Poeciliidae), some males exhibit a mustache-like structure on the upper maxilla, the function of which has not been previously recognized. The mustache consists of epidermal outgrowths at the edge of the scales that appear to have no sensory function. Trait expression varies within as well as among populations of P. sphenops, but is not linked to male body size polymorphism. In mate choice experiments, female P. sphenops exhibited a visual mating preference for males with mustaches, suggesting that the trait may be sexually selected. Since the mating behavior of P. sphenops involves contact of the male's snout and the female genital region prior to copulation, we hypothesize that the mustache may also convey tactile signals to the female.

Female preference for male lateral projection area in Poecilia reticulata

Environmental Biology of Fishes, 2011

The lateral projection area (LPA) hypothesis was investigated by presenting female guppies, Poecilia reticulata with a series of paired males in three experiments. One trait was held constant in each experiment (dorsal fin size in expt I, body size in expt II, and total LPA in expt III) while body: dorsal fin ratio varied. Females spent more time near dummies of greater body and dorsal fin size in experiments I and II. The preference functions based on the first two sets of stimuli showed a similar pattern: the greater the LPA difference between paired dummies, the stronger the preference for the larger of the two. However, in the third experiment, neither fin size, body size, nor any particular dorsal fin+body size combination was preferred. These findings support the LPA hypothesis suggesting that increased LPA is more stimulating to sexually receptive females, and that females consequently prefer larger males. Preference for increased male dorsal fin size/LPA in both P. latipinna and P. mexicana as demonstrated in previous studies, and the more distantly related P. reticulata (shown here) is consistent with common ancestry of the sensory/ neural systems in females of all three species and perhaps the entire Poeciliid family.