The influence of the mandibles of Diplopoda on the food: a dependence of fine structure and assimilation efficiency

9 Pages·1991·1.9 MB·English

by  Jean-François Ponge

Pedobiologia 35, 108-116 (1991)
Gm.Lav Fischer Vcrlag Jena
Zoologisches lnstitul I (Morphologic/Okologie) der Universitlit Heidelberg, Heidelberg, FRG
The influence of the mandibles of Diplopoda on the food - a dependence
of fine structure and assimilation efficiency
HEINZ-R. K6HLER, GERO ALBERTI, and VOLKER STORCH
With 6 figures
(Accepted: 90-07-20)
1. Introduction
Since the role of soil animals in decomposi1ion is still insufficiently understood (HAGVAR,
1988), it is necessary that the specific mechanisms, by which decomposers function within the
soil subsystem, be investigated more intensely (for reviews see: DICKINSON & PUGH, 1974;
SEASTEDT, 1984). Considering growing problems in soil pollution, a better understanding is
urgently needed.
Diplopoda are among the most important decomposition-enhancing soil animals (EDWARDS,
1974; SCllAEFER,·1988; STRIGANOVA, 1971). They have thus been subject to numerous studies on
soil ecology, including ecophysiology (ANDERSON & BIGNELL, 1982; BOCOCK, 1963; WITTAS
SEK, 1987; WOOTEN & CRAWFORD, 1975). However, these studies have not yet been linked lo
morphological aspects. Notwithstanding these many studies, there is - as with other soil animals
- a great lack in knowledge of the specific ability of soil animals to integrate into the soil
system.
According to ANDERSON & BIGNELL (1982), GERE (1956), KAYED (1978), KONDEVA (1980),
POKARZHEVSKll (1981), STRIGANOVA & RACHMANOV (1972). STRIGANOVA & VALIACHMEDOV
1976), WOOTEN (1974), and WOOTEN & CRAWFORD (1975) various diplopod species are
characterized by different assimilation rates. In the present study, 8 species were compared with
regard to their assimilation rates and it was questioned to what mechanisms these differences
could be asc,ibed.
It has been known for a long time that the relative consumption and the assimilation rate of
arthropods decreases ·.vith increasing body size (e.g.BERTHET, 1971; KON DEV A, 1980; STRIGA
NOVA, 1972). This fact could possibly be related to a higher litter-exploitation rate of the smaller
anLmals.
Since the mandibles of diplopods evidently are highly complex organs (ENGHOFF, 1979;
KOHLER & ALBERTI, 1990) and the only masticating structures, it was hypothesized that they are
responsible for the different assimilation efficiencies.
2. Material and methods
Adulls of the following species were examined: Glomeris marginata (VJLLERS. 1789) (Glomeridae), Craspedo
soma t1/ema1111icwn VERHOEFF, 1910 (Craspedosomatidae), Mycogona germanica (VERHOEFF, 1897) lChordeuma
tidae]. Polydesmus angustus LATZEL, 1884 (Polydcsmidae). J11/11s scandi11avills LATZEL. 1884: Cy/i11droi11/us
silvarum (MEINERT, 1868); Ommatoiu/11s rutilans (C. L. KOCH. 1847), and Taclrypodoiulus albipes (C. L. KOCH,
1838) [ lulidae].
Specimens (number in brackets) of G. marginata (13 animals), C. alemannicwn (39). M. germanica (10). P.
a11g11s111s (6), J. sca11di11avius (9), C. si/varnm (7), 0. rutilans (4), and T. a/bipes (4) were kept individually in
plastic boxes on a ground of plaster of Paris. which was constantly held moist. The specimens were fed half-year old
108 Pcdobiologia 35 (1991) 2
leaf litter pieces of Fag11s sy/varica, Casranea saliva, Quercus perraea, and Quercus rubra al a temperature of 15°C.
Since this food had not been sterilized, the effect of the microbial activity has been considered. Therefore, leaf litter
of the tree species mentioned above was cultivated in plastic boxes under the same conditions, but without any
contact lo fauna! components. The mass deficiency obtained under these circumstances was measured. The real
ingested litter mass MN [mg] is then represented by
n (6Ml%J- t.m,1%D·molmg)
M,., [mg] = 2:
100 [%)
i= I
(t.M [%] = perccntal, total mass deficiency of the leaf litter caused by both microbial and diplopod acuvity, 6m,
(%] = percental mass deficiency of the liner caused by microbial activity only, mo [mg]= mass of liner at the time
of 0, n = number of litter pieces).
The faeces were collected daily, oven-dried, and weighed. The mass assimilation rate Am [%) is calculated
by
MF[mg) )
Am[%)= 100 [%]- ---· 100[%]
(
M,.,[mg]
(MF [mg] =total faecal mass).
Since 0. ru1ila11s, J. scandi11avius, and (partly) T. albipes did not accept the food. the essay was repeated with
further decomposed leaf tiller The microbially caused mass deficiency of this litter material was measured in a
'..:parate essay a~ well.
For sc:mning electron microscopy (SEM), the mandibles were prepared by dehydration in 70 % . 95 % , and
100% ethanol. Subsequently, they were transferred into dichlor-difluormethane, critical-point dried. mounted on
Al-stubs, and coated with gold (ROSEl"BAUER & KEGEL, 1978). Furthermore samples of the faeces of all species
mentioned above were oven-dried, mounted, and coated in the same way. Scanning electron microscope: PHILIPS
SEM505.
3. Results
3.1. Nulrition
The different sorts of leaf litter examined showed different palatabilities. The two species of
Quercus, which were ingested in similar quantities, were less attractive than C. saliva. The least
a!lractive species was F. sylvatica. The relative ingestion rate of the litter species are shown in fig.
1. These differences in food preference correlate with the mass deficiency caused by microbial
activity, which was highest in C. sativa and - not regarding the further decomposed litter -
lowest in F. sylvatica (fig. 2).
The assimilation rate of the smallest species was the highest of aU the examjned genera. More
than half of the mass of the ingested material was assimilated by these animals. The exact data are
shown in fig. 6. The big iulid species T. albipes, 0. rutilans, and J. scandinavius showed the
lowest assimilation efficiencies. None of them reached the l l % level. The smaller iulid C.
silvarum, G. marginara, and P. angusrus were intermediate, with assimilation rates between 17 to
31%.
3.2. Morphology
Each mandible of the Diplopoda is divided into three parts, but only the distal part, which has
been called gnathal lobe by ENGHOFF (1979) and MANTON (1979), takes part in crushing the food
into small pieces. The gnathal lobes act against one another and, therefore, the crushing structures
point towards the middle of the oral cavity. The biting apparatus of the diplopod's gnathal lobe
consists of the following substructures: the external and internal teeth, which only roughly cut the
liner particles; the pectinate lamellae; the intermediate area, which bears tiny bristles; and the
molar plate, which squeezes the ingested material (ENGHOFF, 1979; KOHLER & ALBERTI, 1990;
YERHOEFF, 1928).
The substructures of the gnathal lobe most likely determining the size of the ingested particles
are the teeth of the pectinate lamellae. In each of the examined species these teeth are arranged in
a different manner. The iulid species show only 4 pectinate lamellae with a low density of teeth.
Pedobiologia 35 ( 1991) 2 l 09
Fs.
C.s.
60
40
Q.p.
20
Q.r:
0
Ga. Mg. Pa. Ta. C.s. Gm.
Fig. I. Relative ingestion rate of the species accepting the half-year old litter pieces of Fogus sy/l'atica (F. s.).
Cas1a11ea sativa (C. s.), Q11erc11s petraea (Q. p.). and Quercus rubra (Q. r.). C. a.: Craspedosoma ale111a1111ic11111.
C. s.: Cyli11droi11'11f sill'ar111n. G. m.: Glomeris margi11ata. M. g.: Mycogona ger111a11ica. P. a.: Polydes11111s
a11g11s111s, T. a.: Tocl1ypodoi11/11s albipes. m (%): percenlal consumption of litter mas~.
25
20
15
·-
F.s.
10 •
•
-o-
- o- o-
5 0 0 d.l
0
0 30 60 90 120 150 t[d]
Fig. 2. Percent al mass deficiency of the litter caused by microbial activity alone (L'.m, (%]) in dependence of time (t
(d]). C. s.: Castanea satim. F. s.: Fag11s sy/vatica. Q. p.: Quercus petraea, Q. r.: Q11erc11s rob11r, d. I.: funher
decomposed litter material.
I I 0 Pedobiologia 35 ( 1991) 2
hg. 3 Pcc1ina1c lamellae ol the mandible. a: T(lchypodu111/us (l/bipes. b: Cyli1ulro111/11s >tin1r11111, c: ./11/11.1
1t·1111di11al'i11s. d: Ommat11i11/11s r111ila11s. 'quares = 10.000 ~11112
In 0. rurila11s. on the average 22 teeth per JO.OOO ~tm2 were counted; in T. alhipe.1 there is an
average of 33 teeth per I 0.000 run~: in J. sca11di11avi11s there are 28. The ~mailer species C.
.11haru111 bears an average of 58 teeth per 10,000 µm2 (fig. 3).
Three of 1he 9 pectinate lamellae of C. 111argi11aw are characterized by a decreasing number of
1cc1h. However. the remaining 6 show a constant density of 55 teeth per JO.OOO ~tm2 on the
average.
A similar density of teeth was observed in P. a11g11st11s. Although only 6 pectinate lamellae
..:xist in thi~ type. the average number or about 60 teeth per JO.OOO µm2 resembles the situation in
Clomeris.
The smallest species M. germw1ica and C. olema1111icw11 show a much higher density. The 10
pcctinatc lamdlae of M. ger111a11ica consist of an average of 260 teeth per 10.000 rtm2. The teeth
of C. ale111m111irn111. standing in an average density of about 330 per 10,000 µm~. form 10 or 11
pectinatc lamellae (fig. 4).
Correlating with these observations and the assumed masticating function of the gnathal lobes,
the faeces or the compared species showed differences in particle size. Although in each faecal
Pedob1ologia 35 ( 1991) 2 I I I
Fig. 4 Pccun:ne lamellac ol the mandible. a: Glomens mar8i11ata, square = 10.000 111112• b: Cra.1pedusu111a
ah'l11an111c11111. 'quare = 1.000 µm2 c: Mycugo11a germanica. square = I .OOO r1m2. d: Polyde.r11111s a11g11.<111.r,
2
'quare = JO.OOO µm
pellel panicles varied m size, an obvious tendency was observable: the average particle size was
largest in the big iulid species where tooth density is low, and smallest in the smallest species C.
alema1111icum and M. germanica where tooth density is highest. The remaining species occupy
intermediate positions. Thus decreasing particle sizes correlate with increasing tooth densities in
the examined species (fig. 5)
I 12 Pcdobiolog1a JS ( 1991) 2
hg. 5. 1-acccs raniclc> of the examined srccics. a: Tachypodoi11/11s al/Jipes. b: 0111111a11111tl11.1 m11/w1s. c: J11/11,,.
\Ct1tu!t11fl\'lll\, d: Glomen.\ mar1-:i11a/t1, c: Cyli11droiul11!1 dlvor11m. f: Polydc.\·mus angustu\, g: Myco.~tuw gt1rnw11ica.
h Craspedo.101110 t1/1•111a1111in1111. Scale bar = 20 µm.
8 Pcdoh1olog1:1 35 ( 1991) 2 113
Am [X]
Am= 0.198 n + 7.863
80 r=0.93846
60
40
20
0 o--------5·0--------,o~o-------,5•0-------2•0-0_ _____2 _5~0---------1n~o"'µ~J
Fig. 6. Dependence and linear regression of teeth density (n ll0-4 µm-2)) and assimilation rate (Am [%]) in the
examined species. The exact data of assimilation efficiencies arc placed near the abbreviations for the particular
species: C. a.: Craspedosoma alemannicum, C. s.: Cy/iruJroiulus silvarum, G. m.: Glomeris marginata, J. s.: Ju/us
sca11dinavius, M. g.: Mycogona germanica, 0. r.: Ommatoiulus rutilans, P.a.: Polydesmus angustus, and T. a.:
Tachypodoiulus albipes.
4. Discussion
Since no masticating apparatuses can be found in the rather simple gut of the Diplopoda,
mechanical crushing of food can only be ascribed to the mouthparts. It is very likely that the teeth
of the pectinate lamellae mesh with one another to cut the food into small pieces (K6HLER &
ALBERT!, 1990). The acceptance of leaf litter by the animals seems not·to depend strictly on the
litter species. The stage of decomposition appears to be more decisive (BECK & BRESTOWSKI,
1980; SCHMIDT, 1952). According to previous examinations (LYFORD, 1943; NEUHAUSER &
HARTENSTEIN, 1978; SCHMIDT, 1952), Fagaceae showed a lower palatabilily to diplopods than the
leaves of most other tree species. Moreover, freshly fallen leaves of Quercus-species are not
attractive for consumption (BECK & BRESTOWSKJ, 1980; SCHMIDT, 1952). This may result from a
low relative nitrogen content of these leaves. The relative nitrogen content rises with increasing
age due to a more rapid loss of non-nitrogeneous leaf constituents, while the amount of nitrogen
present in the leaves remains relatively constant (ANDERSON, 1973). The acceptance therefore
mcreases with the degree of decomposition and. the correlated decreasing C/N-ratio (BECK &
BRESTOWSKI, 1980; SATCHELL & LoWE, 1967; SCHAEFER, 1988). Thus some litter species reach
the stage of acceptance and consumption by the macroedaphon much earlier than others (EHLERT,
1980).
The ma~s assimilallon efficiency of diplopods varies with temperature. Though GERE ( 1956)
assigned the optimum of assimilation of central European diplopods to only a few degrees above
.20°c, most species prefer a temperature between 0 and 6°C (BOCOCK & HEATH, 1967;
WEGENSTElNER, 1982). Consumption and carbohydrate metabolism decrease above 25°C (BECK
& FRIEBE. 1981; STRIGANOVA & RACHMANOV,1972).
Because of this dependence on temperature, it is difficult to compare the present observations
with other examinations of the assimilation efficiency in Diplopoda. While our data largely agree
with those measured for Iulidae by GERE (1956), KA YEO ( 1978), and KONDEVA ( 1980), higher
values for iulid species were observed under higher temperature and different food conditions
114 Pedobiologia 35 ( 1991) 2
(POKARZHEVSKII, 1981; STRIGANOVA & RACHMANOV, 1972; STRIGANOVA & VALJACHMEDOV,
1976).
As mentioned above the tendency towards a higher assimilation rate at a smaller body size by
some arthropod taxa was confirmed for diplopods. Our data show distinctly that smaller animals
such as C. alemannicum or M. germanica significantly assimilate more effectively than larger
fonns such as lulidae or Glomeridae. Even within the Iulidae, the assimilation efficiency clearly
decreases with increasing size (C. silvarum > J. scandinavius > 0. rwilans > T. albipes). An
increased metabolism of smaller arthropods was already assumed by BERTHET (1971), and was
confirmed for the assimilation rate of diplopods (KONDEVA, 1980; STRJGANOVA, 1972).
This effect may result from a more effective digestion due to a better mastication of the
ingested litter. The relative surface area of the food particles increases with smaller size caused by
finer grinding. Thus digestive enzymes can more easily attack the ingested material.
Since the teeth of the pectinate lamellae are most likely responsible for the size of the ingested
food particles, as recently assumed by KOHLER & ALBERTI (1990) and confirmed by the present
observations of the faeces by SEM, the density of these size-determining structures may be taken
as a substitute for the food particle's size. Thus the linear correlation between the density of the
teeth on the pectinate lamellae and the assimilation efficiency confirms the mentioned depen
dence. This relation, however, is not the only parameter determining assimilation. The enzymatic
equipment must be taken into consideration as well. Thus the deviating results obtained from P.
angustus may reflect the presence of cellulolytic activity in this species (BECK & FRIESE, 1981),
which is ascribed to only few species of the soil macrofauna.
5. Acknowledgements
The authors arc grateful to Prof. Dr. N. PAWELETZ (Dcpanment of Cell Biology, Gennan Cancer Research
Center, Heidelberg) for the use of the SEM and Mr. D. RUSSELL for the English correction.
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IG1R,\KD) <Diplopodal Oecologia 20. 231-236
ynopsis: On11111al .IC 1<•1111jic paper
K01111 R. H -R. G. Al Bl'RTI. and V. STOKC'll. 1991 The innuencc ofihc mandible' ol Diplop11da on 1hc food - a
dcpcndcncl.' of fine 'lructurc and a"imolmion cffic1ency. Pedobiologia 35. 108- 116
The J,.»imila1111n rate' ol 8 ecnlral European species from diffcrcn1 diplopod familic' wcn: mca,ured by feeding
wnh natural leaf loller. Funhermore. 1he rinc '1ruc1ural fealUres of the m:rncloblc'< gnalhal lobe and the facce' of !he
m.:n11oned spccoe' "ere cxamoned b) SEM
The average value, of the ""'molalion rates 'how a linear dcpcncknl'c on !he 1nn1h den>1I) nl !he pcc·1111:11e
lamcll;oe on !he gna1h:il lnbc. Th.: h!Clh or !he pcctinalc lamellac lllOSI likely determine lhc !'nod site.: The highc,1
·"'11nila11on rail' corrc,p<ind, 10 1hc "nallc,1 >izc of loller panicJc,. Within 1hc examined 'pccoc'. lhe highc,1 lt\Olh
density and 1hc h1ghc<.1 a,~i111il:11ion cfllciency occur in the s111alles1 animals.
Key words: Doplnpoda. assimila1ion. mandible. gna!hal lobe. pcc1ina1e Jamcllac. finc-,1ruc1urc.
,\dress of the aulhors: H.-R. KOHLER. G. ALn~.RTl. and V. S1011cH. /.uolugoso.:hc' l11s111u1 I (Morphngi.:/
Okulnl!oc) clcr Univer,niil I leidelbcrg. Im Neuenheimer Feld 230. D IW) -6900 Hcidelbcrg. FRG
I 16 Pcdob1olog1a 35 ( 1991 I 2