Messina Frank J
Department of Biology, Utah State University, 84322-5305, Logan, UT, USA.
Oecologia. 1991 Jan;85(3):447-455. doi: 10.1007/BF00320624.
Populations of the seed beetle Callosobruchus maculatus differ genetically in several traits that mediate intraspecific competition. This study examined competitive interactions between larvae from two strains that differed in their propensity to oviposit on occupied hosts. In a strain (S) where females avoided laying >1 egg/seed, larvae were highly competitive; if two larvae entered a small host simultaneously, only one adult emerged. In a strain (I) whose females were "sloppier" in their egg-laying decisions, more than half of the seeds bearing two larvae yielded two adults. If seeds contained one larva from each strain, only one adult emerged per seed, and 70% of these adults belonged to the more competitive S strain. A larva's probability of emergence could be increased if it entered the seed before its competitor. A two-day headstart was needed merely for I larvae to compete equally with S larvae. Competition also affected development time and adult weight, but its effect was highly strain- and sex-specific. Adult life-history traits also differed substantially between strains. Compared to I beetles, S beetles exhibited decreased longevity, lower fecundity, a truncated period of oviposition, and larger egg and body size. Fecundity was linearly related to body size in the I strain, but was largely independent of size in the S strain. When faced with a shortage of hosts, S females (whose progeny are highly competitive) "withheld" eggs and died without depositing 40% of their lifetime supply. In contrast, the fecundity of I females was independent of seed availability. Comparisons with previous studies suggest that both highly uniform egg-laying and strong interference among larvae may be a consequence of chronic association with a relatively small host. Results from the larval competition experiments were used as parameter estimates for a simple, game-theoretic model that postulates interference vs. exploitative strategies. Fitness comparisons suggest that a strategy employing interference competition cannot be invaded by a more exploitative form of competition in a small host.
豆象科昆虫四纹豆象的种群在介导种内竞争的几个性状上存在遗传差异。本研究考察了来自两个品系的幼虫之间的竞争相互作用，这两个品系在已被占据的宿主上产卵的倾向有所不同。在一个品系（S）中，雌虫避免在一粒种子上产超过1枚卵，该品系的幼虫竞争能力很强；如果两只幼虫同时进入一个小宿主，只有一只成虫羽化。在另一个品系（I）中，雌虫在产卵决策上更“随意”，超过一半有两只幼虫的种子能羽化出两只成虫。如果种子中各有一只来自不同品系的幼虫，每粒种子只会羽化出一只成虫，且这些成虫中有70%属于竞争能力更强的S品系。如果幼虫比其竞争者先进入种子，其羽化的概率会增加。I品系的幼虫只需提前两天进入种子就能与S品系的幼虫展开平等竞争。竞争还影响发育时间和成虫体重，但其影响具有高度的品系特异性和性别特异性。不同品系的成虫生活史性状也有很大差异。与I品系的甲虫相比，S品系的甲虫寿命缩短、繁殖力降低、产卵期缩短，且卵和体型更大。I品系的繁殖力与体型呈线性关系，但在S品系中，繁殖力在很大程度上与体型无关。当面临宿主短缺时，S品系的雌虫（其后代竞争能力很强）“保留”卵，最终有40%的终身产卵量未产出就死亡了。相比之下，I品系雌虫的繁殖力与种子可用性无关。与之前研究的比较表明，高度一致的产卵行为和幼虫之间强烈的干扰可能是长期与相对较小的宿主共生的结果。幼虫竞争实验的结果被用作一个简单的博弈论模型的参数估计，该模型假设了干扰策略与剥削策略。适合度比较表明，在小宿主中，采用干扰竞争的策略不会被更具剥削性的竞争形式所取代。
