Krischik V A, Denno R F
Center for Agricultural Biotechnology, University of Maryland, 20742, College Park, MD, USA.
Oecologia. 1990 Jun;83(2):182-90. doi: 10.1007/BF00317750.
Patterns of growth, reproduction, defense (leaf resin) and herbivory were compared between the sexes of the dioecious shrub Baccharis halimifolia (Compositae). Male plants possessed longer shoots and more tender leaves, grew faster, and flowered and senesced earlier than female plants. Levels of leaf nitrogen, water content, and acetone-soluble resin (shown to deter feeding by polyphagous insect herbivores) did not differ between male and female plants. When offered a choice between leaves from male and female plants, adults of two leaf beetles (Chrysomelidae), the monophagous Trirhabda bacharidis and the polyphagous Paria thoracica, both preferred to feed on male leaves. Similarly, the daily fecundity of older females of T. bacharidis was higher when they were fed leaves from male compared to female plants. However, adult survivorship and total fecundity of T. baccharidis did not differ between male and female leaf treatments. We attribute the feeding preference for and slight increase in fecundity on male plants to the tenderness of male leaves. Larvae of the fly Tephritis subpura (Tephritidae) fed exclusively in the sterile receptacle of male flower heads (85% infested), but the phenology was such that pollen production was not adversely affected. Larvae of two other flies Dasineura sp. and Contarinia sp. (Cecidomyiidae) occupied >95% of only female flower heads where they fed among and on the developing seeds. We conclude that foliage-feeding herbivores are unlikely candidates to explain the female-biased sex ratio (59% female) of B. halimifolia plants in the field, and that their preference for male plants is a result of plant characteristics (e.g. rapid growth) that have been selected by some other factor. However, our data on selective floral herbivory in B. halimifolia are in accord with the argument that dioecy reduces the inadvertent loss of flower parts of one sex when herbivores feed on flower parts of the opposite sex.
对雌雄异株的灌木银胶菊（菊科）的两性植株在生长、繁殖、防御（叶片树脂）和食草情况方面的模式进行了比较。雄性植株的枝条更长，叶片更嫩，生长更快，比雌性植株开花和衰老更早。叶片氮含量、含水量和丙酮可溶性树脂（已证明可阻止多食性昆虫食草动物取食）在雄性和雌性植株之间没有差异。当在雄性和雌性植株的叶片之间进行选择时，两种叶甲（叶甲科）的成虫，即单食性的巴氏三瘤叶甲和多食性的胸斑帕里亚叶甲，都更喜欢取食雄性叶片。同样，与取食雌性植株叶片相比，巴氏三瘤叶甲老龄雌性成虫取食雄性植株叶片时的每日繁殖力更高。然而，巴氏三瘤叶甲成虫的存活率和总繁殖力在雄性和雌性叶片处理之间没有差异。我们将对雄性植株的取食偏好和繁殖力的轻微增加归因于雄性叶片的嫩度。紫腹实蝇（实蝇科）的幼虫只在雄性头状花序的不育花托中取食（85%受侵染），但其物候期使得花粉生产没有受到不利影响。另外两种实蝇Dasineura sp.和Contarinia sp.（瘿蚊科）的幼虫仅在超过95%的雌性头状花序中取食，它们在发育中的种子之间和种子上取食。我们得出结论，以叶片为食的食草动物不太可能是解释野外银胶菊植株雌性偏多的性别比例（59%为雌性）的原因，而且它们对雄性植株的偏好是由一些其他因素选择的植物特征（如快速生长）导致的。然而，我们关于银胶菊选择性花部食草作用的数据与雌雄异株减少当食草动物取食异性花部时某一性别的花部意外损失这一观点一致。
