ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
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Adult female feeding preference & nymph performance 49<br />
Tannins were measured with the radial diffusion method (RDM; Hagerman 1987). The RDM is a<br />
protein-binding assay that can be used to determine the amount <strong>of</strong> both condensed and hydrolysable<br />
tannin albeit the method is more sensible to hydrolysable tannins (Hagerman 1987). The tannic solution<br />
is placed in a petry dish with a bovine serum albumine (BSA) containing agar. As tannin diffuses into<br />
the gel it reacts with BSA and protein precipitation becomes visible as a ring. The area <strong>of</strong> the ring is<br />
proportional to the tannin content <strong>of</strong> the extract.<br />
Both total phenols and tannins were measured from 5 leaves <strong>of</strong> 14 plant species each, and from 20<br />
leaves for P. marginatum (see Table 4-2). For extractions I used approximately 50 mg dry leaf material.<br />
Price and Butler phenolics and tannins are reported as percent Tannic Acid Equivalent (% TAE) per g<br />
dry leaf weight derived from standard curves using tannic acid as a standard.<br />
4.2.2 Dual-choice feeding trials with M. diocles adult females<br />
The synchronous <strong>of</strong>fer <strong>of</strong> food alternatives is a way to reveal the relative preference for a given plant<br />
(e.g., Krebs 1989). To assess preference <strong>of</strong> adult M. diocles females I performed dual-choice feeding<br />
trials. In such a design preference for a plant species (tested species) is expressed as relative preference<br />
in comparison to a fixed reference plant species (Richardson & Whittaker 1982). In varying test plant<br />
species dual-choice tests <strong>of</strong>fer the possibility to assess a food rank order.<br />
M. diocles females were presented with leaves <strong>of</strong> two different plant species: Piper marginatum always<br />
served as reference, while the test plant species varied. I decided for P. marginatum for two reasons: (1)<br />
In field records M. diocles pro<strong>of</strong>ed to be highly associated with plants <strong>of</strong> the genus Piper, in particular<br />
with P. marginatum (cf. Chapter 2). And (2) P. marginatum pro<strong>of</strong>ed to have the leaves with lowest<br />
toughness (see Figure 4-2). According to Coley & Barone (1996) leaf toughness may be the strongest<br />
herbivore defense and consequently the plant species with lowest toughness should be preferred. In a<br />
pre-study I measured leaf toughness <strong>of</strong> 11 host-plant species (see Chapter 4.2.1): P. marginatum had the<br />
lowest leaf toughness (Table 4-1).<br />
Test animals were caught in the field or reared in a laboratory population. As feeding behavior <strong>of</strong> adult<br />
<strong>phasmids</strong> may reflect prior feeding experience (Cassidy 1978; Sandlin & Willig 1993), animals in the<br />
lab were fed with all according food plant species simultaneously.<br />
I tested preference <strong>of</strong> M. diocles females for 12 Piper and two Philodendron test plant species. Leaves<br />
for feeding trials were collected in the vicinity <strong>of</strong> the BCI laboratory. No more than three leaves were<br />
collected per plant individual to cover intraspecific variation in leaf characters. Leaves were put in a<br />
plastic zip log bag, which then was kept on ice in a cooler to keep the leaf material fresh. Between every<br />
following step in handling the leaves were stored coolly.<br />
Leaves first were marked individually using a waterpro<strong>of</strong> marker. Then every leaf was cut in two along<br />
the midrib. The half attached to the midrib was used for the feeding trial. Its area was measured using a<br />
Leaf Area Meter LI-3100 (LI-COR inc., Lincoln, USA) on 1 mm 2 area resolution. Both the share <strong>of</strong> the<br />
reference and the test leaf were put together with their petioles sticking in a water filled vial being