ecology of phasmids - KLUEDO - Universität Kaiserslautern

Adult female feeding preference & nymph performance 72
only function against M. diocles in some Piper host species and even only in particular individuals (as
represented by intraspecific absence of tannin in some leaves) if they had higher tannin contents as
found here. Coley (1986) suggested that such intraspecific tannin variation could be governed
genetically as she found between-plant differences in Cecropia tannin content persisted through time.
Undoubtedly, tannin can deter herbivores: low tannin Cecropia plants suffered five times higher
herbivory by caterpillars than plants with high tannin contents (Coley 1986). This difference in
herbivory was based on substantial differences in tannin concentrations among of Cecropia individuals
(13 to 58 mg*g -1 dw, Coley 1986). High tannin concentrations involve high costs as they have large
initial construction costs and cannot be reclaimed upon leaf senescence (McKey 1979, Coley et al.
1985, Coley 1988).
Considering that tannins had to be accumulated in much higher concentrations compared to other
phenolic compounds to deter M. diocles nymphs, evolution in Piper biochemistry may have favored
qualitative defenses, particularly as many Piper species are gap adapted (Croat 1978). Coley et al.
(1985) suggested that gap adapted plant species (pioneers, high light) should invest carbon in growth
and less in carbon-based defense such as tannins. The rare presence of tannins in Pipers as demonstrated
here and earlier (Baldwin & Schultz 1988) gives support to this view.
However, as all phenolic compounds are based on carbon, the resource availability theory of Coley et
al. (1985) also predicts low levels of total phenols in pioneer species. Baldwin & Schultz (1988) showed
that independent from habitat Piper species shared low levels of total phenols while Miconia forest
species (persistent, low light) had almost 17 times more phenols than Miconia gap species. In this study,
the prediction of similarly low phenol contents among Piper species cannot be supported as total
phenols varied significantly among species (independent from habitat as P. marginatum, P. culebranum;
P. dilatatum, P. hispidum, P. peltatum and P. reticulatum represent pioneer species).
Nevertheless, there is more support for a qualitative defensive pathway in Pipers. The genus Piper is
enormously rich in secondary compounds (reviewed in Sengupta & Ray 1987; Parmar et al. 1997; Dyer
et al. in press). So far in 112 out of more than 1000 species that have been investigated 661 different
compounds have been found (Dyer et al. in press). Several studies have presented effects of all classes
of Piper compounds against herbivores with Amides being particular strong (Bernard et al. 1995;
Parmar et al. 1997 and references therein; Siddiqui et al. 2000; Dyer et al. 2003). For example, Dyer et
al. (2003) showed that three Amides of Piper cenocladum all negatively influenced larval performance
of lepidopterans with stronger synergistic effects of a mixture of the Amides. Given the large variety in
secondary compounds in Piper, the presented preference-performance pattern of M. diocles may have
resulted from interspecific qualitative differences in phenolic composition, with plant species that were
disliked by adults or where nymphs suffered reduced performance containing particularly toxic
compounds. This suggestion is supported by the fact that secondary compounds in Piper differ
qualitatively among species (Parmar et al. 1997). Many species contain exclusive compounds and have
evolved high varieties in particular compound classes (Dyer et al. 2003). To exemplify, from Piper