Comparative Morphometry of Wax Runners and Non Wax Runners

Workers of the different Crematogaster (Decacrema) morphospecies associated with Macaranga are closely related and morphologically similar. We did not find any qualitative difference in leg and tarsus structure between wax running and non-wax running morphospecies. Quantitative morphometry, however, revealed strong interspecific variation of the total leg length, with wax runners (Crematogaster [Decacrema] mspp. 2 and 6) having longer legs than the non-wax runners (Crematogaster [Decacrema] mspp. 3 and 4) (Figure 8.6). To test this effect for significance, we performed analyses of covariance (ANCOVA) on log-transformed data with body mass as the covariate. Because the ANCOVA assumption of parallel regression lines was violated for the middle and hind legs (P < 0.01), we performed analogous analyses with log (pronotum width) instead of log (body mass) as the covariate (regression slopes not significantly different from each other for the front and middle legs, F3181 < 2.6, P > 0.05, but for the hind legs: P = 0.025). All the three leg pairs yielded significant effects (F3184 a 115.1; P < 0.001). Interspecific post hoc

Crematogaster (Decacrema) A msp.2 ■ msp.3 ▲ msp.4 □ msp.6

D D a--'" ^ " " -rf- A A. A ^ , - * *

■ ^

^ AI 4

-"A

A

Non-wax runners

A

A

Log (body mass)

Log (body mass)

FIGURE 8.6 Double logarithmic plot of middle leg length vs. dry body mass in two wax running species (Crematogaster [Decacrema] msp.2 and 6) and two species of non-wax runners (Crematogaster [Decacrema] msp.3 and 4). Data represent a total of 205 ant workers from 29 colonies (n > 32 ants and n > 4 colonies in each morphospecies); lines show model II (reduced major axis) regressions.

TABLE 8.1

Results of ANCOVA Comparing Leg Length between Four Crematogaster (Decacrema) morphospecies with Pronotum Width as the Covariate

Crematogaster Front Legs Middle Legs Hind Legs

TABLE 8.1

Results of ANCOVA Comparing Leg Length between Four Crematogaster (Decacrema) morphospecies with Pronotum Width as the Covariate

(Decacrema)

[Mm]

[Mm]

[Mm]

msp.2 (wax runner)

1700

a

1997

a

2351

a

msp.3 (non-wax runner)

1465

b

1690

b

1975

b

msp.4 (non-wax runner)

1445

b

1628

c (b)

1915

c (b)

msp.6 (wax runner)

1700

c

2181

a

2599

d (a)

Note: Numbers indicate the back-transformed adjusted means of leg length, and the letters indicate the Scheffe grouping. Different letters denote significantly different leg lengths at the 5% level, and letters in parentheses denote significantly different leg lengths at the 0.1% level.

Note: Numbers indicate the back-transformed adjusted means of leg length, and the letters indicate the Scheffe grouping. Different letters denote significantly different leg lengths at the 5% level, and letters in parentheses denote significantly different leg lengths at the 0.1% level.

comparisons revealed highly significant differences in leg length between Crematogaster (Decacrema) mspp.2, 6 and mspp.3, 4 but weaker or no effects within each group (Table 8.1). Thus, the investigated ant morphospecies can be grouped into wax runners and non-wax runners based solely on their leg lengths.

FIGURE 8.7 Two-leg model of ant climbing up a vertical stem. (A) Stem cross section (i.e., view from above). (B) Side view. D: stem diameter; d: lateral distance between tarsi of a leg pair; F±: force perpendicular to stem surface; Fy: force parallel to stem surface; FG: gravity force; s: (vertical) distance between front and hind legs; CG: ant's center of gravity; h: height of center of gravity above stem.

FIGURE 8.7 Two-leg model of ant climbing up a vertical stem. (A) Stem cross section (i.e., view from above). (B) Side view. D: stem diameter; d: lateral distance between tarsi of a leg pair; F±: force perpendicular to stem surface; Fy: force parallel to stem surface; FG: gravity force; s: (vertical) distance between front and hind legs; CG: ant's center of gravity; h: height of center of gravity above stem.

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