Why does herbivore sex matter? Sexual differences in utilization of Fucus vesiculosus by the isopod Idotea baltica

Abstract

O. 2001. Why does herbivore sex matter? Sexual differences in utilization of Fucus 6esiculosus by the isopod Idotea baltica. -Oikos 93: 77 -86.Optimal feeding is often constrained by predation avoidance, which may direct feeding to take place on more sheltered, but less profitable, parts of the habitat. Though constrained, feeding preferences and/or digestive capabilities should coevolve with the energetic and nutritional needs of the animal. These needs, as well as risk taking for these goals, may differ between the sexes. We studied sexual differences in the utilization of the brown alga Fucus 6esiculosus by the marine isopod Idotea baltica. In a feeding preference test with small pieces of alga both sexes prefer the apical, newly grown parts to the basal parts. However, males show stronger preference than females. When isopods are reared on the apical or basal part of the alga alone, sexes grow differently on these parts. Females gain weight equally well and their intermolt duration is the same on both parts of the alga, while males perform clearly worse on the basal than on the apical part. Despite the better quality of the apical parts of the alga, in a grazing experiment in a ''semi-natural'' environment with whole bushes of F. 6esiculosus also the basal parts are consumed, and even preferred over apical parts by females. We suggest that feeding preferences are subordinate to microhabitat choice, and therefore predation avoidance constrains optimal feeding. We hypothesize that the better ability of females than that of males to utilize the basal parts of the alga for growth is a co-adaptation to their risk-averse general reproductive strategy. We discuss the sexual differences in host plant utilization in the context of reproductive strategies of the sexes, especially different risk sensitivity of foraging, and its potential consequences on plant-herbivore interaction.

Macroalgas varadas sobre la superficie de una playa arenosa del sur de Chile: preferencias alimentarias y de habitat de juveniles y adultos de Orchestoidea tuberculata (Nicolet), (Amphipoda, Talitridae)

“…Por ejemplo, Jormalainen et al (2001) sugieren que tanto las diferencias en desarrollo gonadal y tasas de crecimiento entre machos y hembras del isópodo Idotea baltica (Pallas), podrían explicar en parte, las diferencias que muestran esos estados en el consumo del alga parda Fucus vesiculosus Linnaeus en la costa sur de Finlandia. Mientras los machos prefirieron y se desarrollaron mejor consumiendo los brotes nuevos de la zona apical del alga, las hembras se desarrollaron de forma similar consumiendo brotes, tanto de la zona apical como de la zona basal de la misma, e incluso prefirieron esta última zona del alga, a pesar de la mejor calidad nutricional de la zona apical (Jormalainen et al 2001). De este modo, los diferentes requerimientos nutricionales y de energía necesarios para crecimiento y desarrollo gonadal, podrían explicar las diferencias en los patrones de preferencia de juveniles y adultos de O. tuberculata.…”

“…A su vez, el daño estructural producido en las macroalgas por invertebrados epibénticos, es el principal factor biológico que influye en esos desprendimientos (Dayton et al 1984). Las frondas a la deriva o aquellas depositadas en ambientes intermareales costeros, pueden encontrarse en estado fresco o en proceso de embargo, las preferencias alimentarias no solo están en función de la calidad nutricional del alimento, ya que factores tales como competencia y riesgo de depredación pueden restringir la elección de una dieta óptima (e.g., Duffy & Hay 1991, Bednekoff 1996, Jormalainen et al 2001. Por ejemplo, Jormalainen et al (2001), estudiaron los patrones de alimentación del isópodo Idotea baltica (Pallas) en la costa de Finlandia y encontraron que la elección de la dieta de las hembras estuvo subordinada al riesgo de depredación.…”

CONTENTS OF SOLUBLE, CELL-WALL-BOUND AND EXUDED PHLOROTANNINS IN THE BROWN ALGA Fucus vesiculosus, WITH IMPLICATIONS ON THEIR ECOLOGICAL FUNCTIONS

“…Individuals live for many years, so most of the thallus is nongrowing tissue. In our study area, the alga has only one important herbivore, the isopod I. baltica; this is a generalist feeder, but prefers F. vesiculosus over other potential host species (Jormalainen et al, 2001).…”

Effect of Reproductive Status on the Diet Composition of Wolverines (Gulo gulo) in Boreal Forests of Eastern Finland

“…Sex differences in foraging ecology have indeed been found in a variety of taxa (e.g. Ligon 1968, Clutton-Brock et al 1983, Jormalainen et al 2001.…”