Bryant is both the author and photographer for today’s entry. He writes:
Today’s image was taken in the David C. Lam Asian Garden, here at the UBC Botanical Garden. This dioecious evergreen shrub is native to temperate and tropical Asia (China, Japan, India and Malaysia). I was tipped off to go look at this plant by Douglas Justice (Associate Director and Curator of Collections at UBCBG). At first I had trouble finding the plant as it was slightly hidden behind a couple rhododendrons but I definitely had no trouble smelling it. Eurya japonica gives off a pungent aroma that could be described as metallic or zinc-like mixed with hints of ammonia and carrion, which I became familiar with while taking this image. This member of the Pentaphylacaceae grows to about 3m high. Plants have serrated leaves that appear in a herringbone formation. For another image of the branch/flower morphology and some interesting information on its taxonomic relationships, see the previous BPotD post on Eurya japonica.
Eurya japonica is known to be sexually dimorphic, meaning male and female plants are morphologically different in additional ways beyond the physical structure of the reproductive organs. Sexual dimorphism is fairly common among dioecious plants, and when dimorphism involves defense mechanisms we tend to think primarily of leaves, thorns and prickles (vegetative tissues). However, there have been an increasing amount of studies on defense mechanisms against florivory (flower-eaters). Eurya japonica is the subject of one such study concerning the chemical defense of its female flowers; see: Tsuji, K. and Sota, T. 2010. Sexual differences in flower defense and correlated male-biased florivory in a plant-florivore system. Oikos, 119: 1848-1853. doi: 10.1111/j.1600-0706.2010.18585.x.
In this case, the male flowers were observed to be eaten much more frequently than the female flowers by the florivorous larvae of the geometrid moth Chloroclystis excisa. This phenomenon was observed both in the wild and under controlled experimental conditions. In the wild, adult moths only deposited their eggs on male flowers. When eggs were deposited on the female flowers/buds of Eurya japonica in captivity, all of the resulting larvae that fed on the calyx of the female flower did not survive. This is believed to be due to higher concentrations of phenolic compounds and condensed tannins that occur in the female flowers. Generally, florivory of male flowers seems to be more prevalent than florivory of female flowers among sexually polymorphic plant species. Although there are some theories as to why this may be, there is much to be learned about the co-evolution of flowers and florivores and what truly makes sex-based selection occur.
For more reading relating to Eurya japonica and geometrid moth interactions see:
Kaoru Tsuji & Teiji Sota. 2011. Geographic variation in oviposition preference for male and female host plants in a geometrid moth: implications for evolution of host choice. Entomologia Experimentalis et Applicata. 141: 178-184.
For further reading on male-biased herbivory, see:
Lorne M. Wolf. 1997. Differential Flower Herbivory and Gall Formation on Males and Females of Neea psychotrioides, a Dioecious Tree. Biotropica, 29: 169-174.
Krupnick, G. A. et al. 1998. Floral herbivore effect on the sex expression of an andromonoecious plant, Isomeris arborea (Capparaceae). Plant Ecology. 134:151-162.