Quantitative variation of secondary metabolites in the sea hare Aplysia parvula and its host plant, Delisea pulchra

Self Cite

Although sea hares are well known for acquiring algal secondary metabolites from their diet, the effects of diet on fitness and the susceptibility of sea hares to predators are poorly understood. We examined the effects of diet on the performance of the sea hare Aplysia parvula, and measured predation by reef fishes on sea hares raised on different seaweeds. Diet-switching, body size, the presence of conspecifics, and the presence of epiphytes on dietary algae were also investigated experimentally. A. parvula were fed the chemically rich red algae Delisea pulchra or Laurencia obtusa in laboratory experiments, and consumption, growth, egg production, conversion efficiency, and survivorship were measured. Sea hares fed L. obtusa consumed more algae, grew faster, laid more eggs, and had higher survivorship compared to sea hares fed D. pulchra. Most other factors investigated -body size, the presence of conspecifics or epiphytes -were in general unimportant relative to the effects of diet. The disparity in fitness of A. parvula fed D. pulchra versus L. obtusa is primarily due to different levels of consumption of each seaweed, as conversion efficiencies were similar. Predation on sea hares raised on different diets and containing different types and levels of acquired secondary metabolites was measured in field experiments in which sea hares were exposed to mixed assemblages of reef fishes. A high proportion of both chemically rich (fed red algae) and chemically poor sea hares (fed the green alga Ulva sp.) were eaten by fishes (with predation rates of 25 to 55% over 1 to 2 h), although this sea hare was relatively unpalatable compared to squid tissue. Juvenile A. parvula were eaten at a significantly greater rate than adults. Sea hare ink did not deter some fishes, which consumed both de-inked and untreated sea hares. Predation by fishes was similar in adjacent habitats, but varied between sites, and was not restricted to A. parvula as reef fishes also ate juvenile A. dactylomela of equivalent size. The benefit A. parvula gain from acquiring algal secondary metabolites is unclear, as these compounds appear ineffective as defences against some fishes. A. parvula may sequester algal secondary metabolites as part of a broader defensive strategy that includes crypsis and escape movements.

Section: Introductionsupporting

confidence: 51%

Section: Predation By Fishesmentioning

confidence: 90%

Effects of algal diet on the performance and susceptibility to predation of the sea hare Aplysia parvula

Rogers¹,

Nys²,

Steinberg³

2002

Self Cite

“…Concentrations of secondary metabolites are generally higher at distal portions in algae, soft corals, gorgoni-ans, and trees (Coley 1983, Harvell & Fenical 1989, Wylie & Paul 1989, Meyer & Paul 1995, de Nys et al 1996, but see . Structural materials usually follow a contrasting pattern, decreasing in concentration from the distal end to the base.…”

Section: Discussionmentioning

confidence: 99%

Intracolonial variation in chemical defenses of the sponge Cacospongia sp. and its consequences on generalist fish predators and the specialist nudibranch predator Glossodoris pallida

Becerro¹,

Paul²,

Starmer³

1998

On Guam, the nudibranch Glossodoris pallida specializes in feeding on the branching sponge Cacospongia sp., which contains scalaradial and desacetylscalaradial as major secondary metabolites. The nudibranch, which accumulates both compounds for its own defense, is typically found on the base of the sponge. In this study, we quantified intracolonial variation in the production of secondary metabolites (percent yield of crude extract, filtered extract, scalaradial, and desacetylscalaradial), structural material (fiber and ash content), and protein content in Cacospongia sp. in order to assess the consequences that such variation has on feeding responses of generalist fish predators, the specialist nudibranch predator G. pallida, and on the distribution of the nudibranch on the sponge. Levels of secondary metabolites varied among the parts of the sponge analyzed (tip, base, surface, and matrix). The mean peicer,: y-ic!d of cr. ; dc cx!:zct :vs: $isher i?, the surface nf !he spc~cje. .uhi!e filtered extract and desacetylscalaradial were higher in tips than in bases Structural materials were highest in the base and in the surface of the sponge. In contrast, the inner part of the sponge contained higher levels of protein than the surface, but no differences were found between tips and bases. Compared to a control, the crude extract of Cacospongia sp. significantly deterred fish feeding at the lowest concentration found in the sponge (base concentration) In field assays. When offered a cholce between base and t~p concentrations, both the pufferfish Callthiyaster solandn in laboratory assays and the natural reef fish assemblage in the field showed no preference for extracts of bases over tips (i.e. lower levels over higher levels of chemical defenses). However, when offered a choice between pieces of sponge from the base and from the tip, the nudibranch G. pallida preferred bases over tips, which agrees with the nudibranch distribution on the sponge. Alternative factors may shape the observed distribut~on of nudibranchs on Cacospongia sp. Nudibranchs at the bases may suffer lower levels of predation because they are less accessible to predators than nudibranchs at the tips of the sponge Therefore, we also tested whether small disks of artificial squid food located on tips and bases of the sponge are equally accessible to generalist fish predators. The reef fish C. solandri in laboratory assays and the natural fish assemblage at the Cacospongia sp. community consumed equal amounts of food from tips and bases. Our data demonstrate that Cacospongia sp. extracts deter feeding by fishes at the lowest concentration found in the sponge, which suggests that the higher concentration in the tips is not a mechanism to avoid consumption by generalist fish predators. In contrast, avoidance of higher levels of chemistry appears to be the factor behind the selection of bases over tips by the specialist nudibranch predator G. pallida. Intracolonial variation in chemical defenses seems to determine the nudibranch distribution o...

“…While several studies have examined quantitative variation in algal secondary chemistry (Carlton et al 1989, 1995, de Nys et al 1996, Puglisi & Paul 1997, Matlock et al 1999, few have examined the effects of within-algal variation on the feeding preferences of mesograzers (Van Alstyne 1989, Poore 1994, Cronin & Hay 1996a. Such studies are necessary not only to understand the factors affecting the production of chemical defenses, but also to provide insight into the ecological consequences of such variation (Hay 1996, Becerro et al 1998.…”

Section: Introductionmentioning

confidence: 99%

“…The sea hare Aplysia parvula is an oligophagous herbivore that feeds primarily on red algae (Carefoot 1987, Rogers et al 1995 and is able to sequester algal metabolites from its diet that have been hypothesized to function in defense against predators (Faulkner 1992, de Nys et al 1996. Switzer-Dunlap (1978) reported that, in laboratory cultures, larvae of A. parvula preferentially metamorphose in the presence of Portieria hornemannii (= Chondrococcus hornemanni) relative to other algae.…”

Section: Introductionmentioning

confidence: 99%

Chemical defenses in the sea hare Aplysia parvula: importance of diet and sequestration of algal secondary metabolites

Ginsburg¹,

Paul²

2001

Marine algae produce a variety of secondary metabolites that function as herbivore deterrents. Algal metabolites, however, often fail to deter damage by some herbivores such as mesograzers that both live and feed on their host alga. In addition, the degree to which intraspecific chemical variation in an alga affects a mesograzer's feeding behavior and its ability to deter predators is poorly understood. The red alga Portieria hornemannii contains the secondary metabolites apakaochtodene A and B, which have been shown to vary in concentration among sites on Guam and act as significant deterrents to fish feeding. On Guam, the sea hare Aplysia parvula preferred and grew best when fed its algal host P. hornemannii. However, high concentrations of P. hornemannii crude extract and the pure compounds apakaochtodene A and B acted as feeding deterrents to A. parvula. Despite differences among sites in the levels of apakaochtodenes A and B, A. parvula showed no significant preference for P. hornemannii from any one location. Aplysia parvula found on P. hornemannii sequestered apakaochtodenes, and both whole animals and body parts were unpalatable to reef fishes. Sea hares found on the red alga Acanthophora spicifera, which contains no unpalatable secondary metabolites, had no apakaochtodene compounds and were eaten by fishes. This observation is consistent with the hypothesis that diet-derived algal metabolites in sea hares play a role in deterring predation.