To feed or to breed: morphological constraints of mouthbrooding in coral reef cardinalfishes

Abstract

Functionally coupled biomechanical systems are widespread in nature and are viewed as major constraints on evolutionary diversification, yet there have been few attempts to explore the implications of performing multiple functions within a single anatomical structure. Paternally mouthbrooding cardinalfishes present an ideal system to investigate the constraints of functional coupling as the oral jaws of male fishes are directly responsible for both feeding and reproductive functions. To test the effects of (i) mouthbrooding on feeding and (ii) feeding on reproductive potential we compared the feeding apparatus between sexes of nine species of cardinalfish and compared brood characteristics among species from different trophic groups, respectively. Mouthbrooding was strongly associated with the morphology of the feeding apparatus in males. Male cardinalfishes possessed longer heads, snouts and jaws than female conspecifics irrespective of body size, trophic group or evolutionary history. Conversely, reproductive potential also appeared to be related to trophic morphology. Piscivorous cardinalfishes produced larger, but fewer eggs, and had smaller brood volumes than species from the two invertebrate feeding groups. These interrelationships suggest that feeding and reproduction in the mouth of cardinalfishes may be tightly coupled. If so this may, in part, have contributed to the limited morphological diversification exhibited by cardinalfishes.

Sexual dimorphism in the feeding mechanism of threespine stickleback

“…Sexual dimorphism in trophic structures is known in several fish groups (Feduccia and Slaughter, 1974;Barnett and Bellwood, 2005;Albert and Crampton, 2009;Hoey et al, 2012) and is suspected in others, but our findings are the first to demonstrate sexual dimorphism in feeding kinematics. It is particularly interesting that one of the major differences between male and female stickleback is in jaw protrusion, a trait that has long been thought to impact various aspects of feeding ability (Schaeffer and Rosen, 1961;Motta, 1984) and was recently shown to play a major role in determining suction-feeding performance (Holzman et al, 2008;Holzman et al, 2012).…”

“…Conversely, behaviors such as territory defense, display or brood care may place demands on the trophic apparatus that compromise feeding performance; for example, enlargement of the buccal cavity in mouth-brooding male cardinalfishes could compromise suction-feeding ability (Barnett and Bellwood, 2005;Wainwright et al, 2007). However, despite extensive study of the kinematics of prey capture (Wainwright et al, 2007;Higham, 2007) and divergence in diet and feeding morphology between the sexes (Vincent et al, 2004;Barnett and Bellwood, 2005;Barnett et al, 2006;Hoey et al, 2012), there appear to be no examples of sexual dimorphism in feeding kinematics.…”

RETRACTED ARTICLE: Novel life history strategy in a deep sea fish challenges assumptions about reproduction in extreme environments

“…This lower fecundity in Parazen could be due to natural processes in this species, space constraints in the buccal cavity, or loss of some eggs in the process of capture and preservation. However, smaller clutch sizes in mouthbrooding fishes was suggested to allow for better churning of the eggs for aeration in haplochromine cichlids 35 and increased hypoxia tolerance in cardinalfishes 36,37 .…”

Hydrodynamic drag constrains head enlargement for mouthbrooding in cichlids

“…Many species perform mouthbrooding: a form of parental care where one of the sexes protects and ventilates the eggs inside the mouth cavity [3,[7][8][9], which is often linked to a sexual dimorphism of the head [9][10][11]. As the head also serves as a bow during locomotion, a streamlined shape of the head will increase swimming efficiency by reducing the pressures formed in pushing water aside for the fish to pass.…”