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 48<br />
4.2.1 Measuring leaf traits<br />
Relative leaf toughness, water content, specific leaf weight, total phenol and tannin content were<br />
assessed for mature leaves <strong>of</strong> 15 host plant species <strong>of</strong> M. diocles.<br />
Leaves were collected in the vicinity <strong>of</strong> the BCI laboratories at the forest edge and in the understory. No<br />
more than three leaves were collected per plant individual to cover intraspecific variation in leaf traits.<br />
Leaves were stored in zip log bags in a cooler until measurements were taken.<br />
Data for leaf water content and specific leaf weight derived from leaves used in dual choice feeding<br />
trials and are expressed as species-specific means (for sample size see Table 4-1). For details see<br />
Chapter 4.2.2.<br />
4.2.1.1 Measuring leaf toughness<br />
Coley and Barone (1996) considered leaf toughness as the most effective plant defense. For this reason I<br />
decided to use the M. diocles host plant species with lowest leaf toughness as reference in dual-choice<br />
feeding trials (see Chapter 4.2.2). Consequently I had to measure leaf toughness before starting<br />
preference tests. This initial screening included nine Piper and two Philodendron species. From these<br />
species I collected six leaves from six individuals each in the nearby vicinity <strong>of</strong> the BCI laboratory and<br />
took toughness measurements as described below. Later, when preference tests were already running, I<br />
added four more Piper species. Here, I measured toughness <strong>of</strong> all leaves that were used in dual-choice<br />
feeding trials. For these reasons sample sizes for toughness measurements vary among species (for<br />
sample size see Table 4-1).<br />
Leaf toughness was measured using a Chatillon penetrometer (Chatillon Co. Ltd., New York; rod<br />
diameter = 3.25 mm; one unit represents a force <strong>of</strong> 1 g * 8.3 mm -2 ) (alternative methods are described<br />
by Choong 1996). As I wanted to measure the strength an herbivore needs to cut leaf tissue I had to<br />
assure to minimize tissue flexibility. Therefore each leaf was positioned between two Plexiglas plates<br />
seated on four stands. The Plexiglas plates were perforated with holes <strong>of</strong> 5mm diameter both. Upraising<br />
the plates prevented from flawed measurements as the punching rod may jump back up if it hits a hard<br />
surface directly after having pierced the leaf tissue. From each leaf I took 10 measurements. Mayor leaf<br />
veins were avoided. Toughness was calculated on a relative scale as species-specific mean toughness <strong>of</strong><br />
mature leaves.<br />
4.2.1.2 Leaf phenol and tannin content<br />
To evaluate leaf foliar chemistry freeze-dried leaves from dual-choice feeding trials were ground and<br />
extracted in 70 % aqeuous acetone (Hagerman 1988).<br />
Total phenolics were assayed using the technique <strong>of</strong> Price & Butler (1977) modified by Mole &<br />
Waterman (1994). The reaction is an oxidation-reduction in which the phenolate ion is oxidized and<br />
ferric irons are reduced to the ferrous state forming the Prussian Blue complex. Phenolic content is then<br />
measured spectrophotometrically.