J . Zool., Lond. (1995) 236, 563-569

Functional directional asymmetry in fallow deer (Duma duma) antlers

FERNANDO ALVAREZ

Estacidn Bioldgica Dofiana, C.S.I.C., Aptdo. 1056, Sevilla, Spain

(Accepted 25 May 1994)

(With 2 figures in the text)

The right antlers of fallow deer are significantly more developed than the left antlers with respect to the lengths of the beam, trez tine and palm, as well as antler weight and number of points. The cross-section at the base is also more elliptical in the right antler. The size difference is correlated with the more intense use of right antlers in fighting, and with the greater breadth of the areas of insertion of the neck muscles in the skull’s nuchal region.

Contents

Introduction . . . . . . . . . . . . . . . . . . Material and methods . . . . . . . . . . . . . .

Measurements of antlers and skull’s nuchal region. . Recording and analysis of fighting and displaying . .

Results . . . . . . . . . . . . . . . . . . . . Antlers and neck muscles’ insertion . . . . . . . .

Discussion . . . . . . . . . . . . . . . . . . . . References. . . . . . . . . . . . . . . . . . . .

Use of right and left antlers . . . . . . . . . .

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Page 563 565 565 565 567 567 561 568 569

Introduction

The antlers of fallow deer are palmate and have only two frontal tines, the basal or brow tine and the distal or trez tine. The upper and rear edges of the palm end in a series of points or spellers (Chapman & Chapman, 1975; Bubenik, 1983; Alvarez, 1994) (Fig. 1).

Antlers are used during fighting and sparring, either by clashing the distal palm spellers against those of the opponent at the end of a jump (jumping clash) or, with antlers already in contact, by pushing with them against the opponent’s antlers. The wide palm is also presented to opponents during face to face displays and parallel walking (Alvarez, 1993).

Concerning bilateral asymmetry (the mean value of a character on one side of an individual being significantly larger than the mean of the other side, Leary & Allendorf, 1989), evidence was provided by Riney (1954) for the right antlers of 29 sets from free-ranging fallow deer in New Zealand being consistently larger than their left antlers, while two captive animals showed a significant trend throughout their lives toward higher values of antler weight, beam diameter, and number of points for their right antlers.

Although the possible function of the asymmetry remains unknown, if it is associated with the differential use of the right and left antlers during fights, we should also expect it to occur in the

563

0 1995 The Zoological Society of London

564 F. ALVAREZ

1

3 z

FIG. 1. Some of the measurements taken on fallow deer antlers and skull. (a) Side view of antler. 1: Antler straight length. 2: Basal beam length. 3: Palm length. 4: Length of brow tine. 5: Length of trez tine. 6: Greatest latero-medial diameter at base. 7: Greatest oro-aboral diameter at base. (b) Nuchal view of skull. A: Akrocranion (Most aboral point of vertex of cranium in medial plane). B: Basion (orobasal border of the foramen magnum in median plane, Driesch, 1976). 1: Greatest nuchal breath.

seasonally growing neck muscles inserting on the skull (Field et al., 1985), which play a role in opposing the torques created during antler-to-antler fights (Alvarez, 1993).

The only other reported case of asymmetry in deer antlers refers to reindeer and caribou where the left antler brow tines are larger than the right, at least in early life, if the deer are living in the northern hemisphere (Davis, 1983; Goss, 1983). The function, if any, of this asymmetry remains unknown, as does the cause of its reversal (right brow tine larger than the left) in reindeer living in the southern hemisphere (South Georgia Island, 50"-55" S; Goss, 1983).

The aims of this study are to measure the extent of size difference in the left and right antlers of wild fallow deer, and to elucidate its function.

ANTLERS’ DIRECTIONAL ASYMMETRY

Material and methods

565

Measurements of antlers and skull’s nuchal region

Measurements were taken of 13 trophies (skull with antlers) and of 29 pairs of cast antlers from different individuals (each pair belonging to the same individual) of fallow deer living wild in the National Park of Doiiana (SW Spain). Specimens were collected from the year 1981 to 1991. Immediately after a stag dropped his antlers they were collected and kept in pairs in a dry store for at least one whole year. All antlers belonged to adult stags of 4+ years.

Measurements were taken on each antler as shown in Fig. 1. Linear distances were measured to the nearest mm, except at the antler base, which were to the nearest 0.01 mm.

In addition, the following parameters were obtained for each antler:

Second moment of area (I) (for convenience 4JI) at the seal (basal antler surface). It describes the distribution of material at the antler’s base, where bending stress is highest (Kitchener, 1985; Alvarez, 1990). It was calculated according to:

7ra3b I=- 4

where a = half the cross-section ellipse’s major axis; b = half the cross-section ellipse’s minor axis. Ratio of greatest latero-medial diameter/greatest oral-aboral diameter at antler base: measured with callipers at the junction of the antler and pedicle on the trophies and on the seal on cast-off antlers. Palm area: the area of its outline on a sheet of paper placed against the palm’s outer surface was measured to the nearest cm2 with the aid of a planimeter. Antler weight: Pesola spring balances were used to weigh cast-off antlers to the nearest 10 g interval. Antler bone density: resulting from dividing weight by volume; it was measured to the nearest 10g/cm3 interval. The volume was measured by weighing the cast-off antlers submerged in water (the spongy antler seal plugged up with paraffin paper). Number of spellers: only those measuring at least 1 mm long were considered.

As an indication of the size of the neck muscles inserting into the skull, the breadth from the middle (akrokranion-basion) line was measured to the most distant right and left areas of insertion of the neck muscles into the skull nuchal region of 13 trophies (on the bony ridge in the mastoid region) (Fig. 1).

Recording and analysis of fighting and displaying

Data on the use of antlers during fighting were also obtained from the Doiiana National Park population in 3 successive mating seasons from 1986. Adult fallow deer stags (4+ years) were filmed with a video camera equipped with 400-1200 zoom lenses, whenever at least 2 stags were sufficiently close to each other to expect interactions among them. The duration of the 13 fights recorded varied from 10 to 23 min.

The instances in which the use of the right or left antler could be determined were part of all actions recorded during the following 2 most frequently used fighting techniques and palm displays (Alvarez, 1993): Jumping clash: The protagonist jumps towards the opponent from 0.5-2.5 m and the distal spellers of the antlers of both combatants clash together (Fig. 2). Push: With antlers already in contact with those of the opponent, the protagonist pushes towards him. Usually both antlers make contact, most often on the antler palm (mainly on the spellers or trez tine), and the pushes are oriented mainly in a forward direction, less frequently in rotational or lateral directions (Fig. 2). Palm display: The combatants stand motionless near each other for a few seconds, usually holding their antlers high and often turning the head so as to present the wide outside surface of one palm towards the opponent.

566 F. ALVAREZ

ANTLERS’ DIRECTIONAL ASYMMETRY

TABLE I Average values (fS.0.) of measurement sfor the right and left antlers

561

mean f S.D. n

Antler straight length (mm)

Basal beam length (mm)

Palm length (mm)

Antler surface length (mm)

Length of brow tine (mm)

Length of trez tine (mm)

4JI (mm)

Latero-medial diameter/oro-aboral diameter at base

Palm area (cm2)

Antler weight (g)

Antler bone density (g/cm3)

Number of spellers

Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left

432.0 f 93.4 419.8 f 91.8 238.7 f 28.3 239.4 f 31.1 283.1 f 114.8 276.9 f 112.9 533.2 f 120.5 525.7 f 115.8 98.7 f 42.8 97.2 f 44.1 78.2 f 22.2 63.0 f 24.1 13.9 f 2.1 13.9 f 2.2 0.94 f 0.08 0.96 f 0.08

256.0 f 172.1 249.0 f 180.0 409.1 f 171.0 390.4 f 161.9

1.18 f 0.07 1.22 zk 0.08 8.9 f 3.7 8.2 f 3.6

42**

40NS

35*

33NS

40NS

42***

33NS

42 *

35NS

25*

25**

36*

NS: Not significant; *P<O.Ol, **P<O-OOl, ***P<O.OOOI. Wilcoxon signedranks test, Siegel(1956)

Results

Antlers and neck muscles’ insertion

As can be seen in Table I, right antlers are significantly more developed than left antlers with respect to antler straight length, length of trez tine, palm length, antler weight and number of spellers, but their bone density is less and their basal cross-sections are more elliptical than in the left antlers.

The values for the greatest nuchal breadth (mean f S.D. = 43.4 f 3.4mm) on the right side of the skulls were significantly greater than on the left side (mean f S.D. = 42.6 f 2.7 mm) ( t = 12.5, n = 13, P < 0.02, Wilcoxon signed-ranks test).

Use of right and left antlers

Although both antlers of the protagonist of a jumping clash always come into contact with

FIG. 2. Use of antlers during the most frequent antler-to-antler fighting techniques. (a) Jumping clash. (b) Forward push. (c) Rotational push. (d) Lateral push.

568 F. ALVAREZ

TABLE I1 Percentage of use of right and left antlers when initiating the two most frequentJighting techniques between adult males (number of cases in brackets)

JUMPING CLASH*** (first contact) Right antler Left antler n

PUSH** (all directions) Right antler Left antler Both antlers n

FORWARD PUSH* Right antler Left antler Both antlers n

Right antler Left antler Both antlers n

Right antler Left antler Both antlers n

ROTATIONAL PUSHNS

LATERAL PUSH'

NS: Not si nificant; * P < 0 . 0 5 , **P<O.Ol,

No level of significance because sample size 8 ***P<O.OOl; x test

too small

those of the opponent, one antler touches the opponent's first, and this is most often the right antler (Table 11).

During the push, although usually both antlers of the protagonist are kept in contact with the antlers of the opponent, the protagonist most often pushes with the aid of only one antler, most frequently the right one, much less frequently with the left antler or with both antlers at the same time (Table 11).

Concerning palm display, although there is a significant trend for stags to direct one antler at the opponent ( z = 2.16, n = 94, P < 0.05, signed test), they do not show any significant preference for presenting their right or left antler ( z = 0.39, n = 58 , P > 0.05, signed test).

Discussion

The lower bone density found for the right as compared to the left antlers of fallow deer may be explained as an effect of the negative correlation between the antler length and its bone density, the proportion of cancellous bone increasing distally in the antler palm (Alvarez, 1994).

The higher development of the right antler and of its palm, trez tine and spellers, must provide

ANTLERS’ DIRECTIONAL ASYMMETRY 569

more opportunities for engaging with the antlers of the opponent. The elongation of the antler’s basal cross-section ellipse’s major axis is precisely that presented in the direction of the most forceful fighting technique (jumping clash), while the most frequent direction of push (forward push) corresponds with the more intense use of the right antler during these types of fights.

If, as demonstrated for humans, American martens and house mice (Schoultz, 1937; Jolicoeur, 1963; Leamy, 1984), fallow deer also present directional asymmetry toward greater development of the right forelimb, then this could correlate with the higher development of the right antler, since observations of different deer species with amputated limbs or parts of limbs suggest that each antler’s stage of growth is related to the strength of its set of diagonal legs (the front leg of the same side and the rear leg of the contralateral side). The reason for this could perhaps be the need to keep bilateral balance by head tilting during locomotion, when the whole body weight is supported by a set of diagonal legs (Marburger et al., 1972; Chapman, 1975; Davis, 1983). Fallow deer may have taken advantage of the situation by making preferential use during fights of the right antler and neck muscles, and (according to the description of fighting, Alvarez, 1993) in all probability of the forelimb of the same side.

I am grateful to the guards of Doiiana for their help in collecting deer antlers; to M. Vazquez for assisting measuring specimens and to J. Lopez Rojas for his drawings. Financial support came from research grant PB 87-03 16 of the Spanish CICYT.

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