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Diet and dietary selectivity of the platypus in relation to season, sex and macroinvertebrate assemblages

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The diet of the platypus Ornithorhynchus anatinus was studied by examination of material collected from the cheek pouches of animals captured while foraging in streams in Kangaroo Valley, NSW, Australia. Platypuses consumed benthic invertebrates from 55 families in 16 orders, with virtually no prey being derived from the terrestrial environment. We also sampled invertebrates in pool, riffle and stream edge habitats to identify where prey were obtained. Invertebrates in the diet were most similar to those collected along stream edges and in pools compared with the faster-flowing riffles, suggesting that platypuses focused their foraging activities largely in these deeper water habitats. Although there was no seasonality in the assemblage structure of macroinvertebrates, the diet of platypuses varied between seasons, notably between winter and summer, suggesting that some dietary selectivity is seasonal. Dietary differences between the sexes were not detected. Overall, our results suggest that some dietary selection occurs in the platypus with respect to both foraging habitat and season. Seasonal selectivity may reflect different metabolic demands on platypuses at different times of the year. In contrast, habitat selectivity may reflect difficulty of prey access and risk of prey escape in fast-flowing riffles, higher energy costs and risk of predation associated with exploiting this habitat, and prey avoidance responses that are more rapid in the shallow riffles than in the deeper water pools and stream edges. These alternatives await evaluation by future research.
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Diet and dietary selectivity of the platypus in relation
to season, sex and macroinvertebrate assemblages
T. A. McLachlan-Troup
1
, C. R. Dickman
1
& T. R. Grant
2
1 Institute of Wildlife Research, School of Biological Sciences, University of Sydney, Sydney, NSW, Australia
2 School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, Australia
Keywords
platypus; Ornithorhynchus anatinus; diet;
dietary selectivity; macroinvertebrate;
monotreme; aquatic mammal.
Correspondence
T. A. McLachlan-Troup, Institute of Wildlife
Research, School of Biological Sciences,
A08, University of Sydney, Sydney, NSW
2006, Australia. Tel: +6 12 9351 2318; Fax:
+6 12 9351 4119
Email: mclachlan.troup@gmail.com
Editor: G ¨
unther Zupanc
Received 20 May 2009; revised 13 August
2009; accepted 23 August 2009
doi:10.1111/j.1469-7998.2009.00645.x
Abstract
The diet of the platypus Ornithorhynchus anatinus was studied by examination of
material collected from the cheek pouches of animals captured while foraging in
streams in Kangaroo Valley, NSW, Australia. Platypuses consumed benthic
invertebrates from 55 families in 16 orders, with virtually no prey being derived
from the terrestrial environment. We also sampled invertebrates in pool, riffle and
stream edge habitats to identify where prey were obtained. Invertebrates in the diet
were most similar to those collected along stream edges and in pools compared
with the faster-flowing riffles, suggesting that platypuses focused their foraging
activities largely in these deeper water habitats. Although there was no seasonality
in the assemblage structure of macroinvertebrates, the diet of platypuses varied
between seasons, notably between winter and summer, suggesting that some
dietary selectivity is seasonal. Dietary differences between the sexes were not
detected. Overall, our results suggest that some dietary selection occurs in the
platypus with respect to both foraging habitat and season. Seasonal selectivity may
reflect different metabolic demands on platypuses at different times of the year. In
contrast, habitat selectivity may reflect difficulty of prey access and risk of prey
escape in fast-flowing riffles, higher energy costs and risk of predation associated
with exploiting this habitat, and prey avoidance responses that are more rapid in
the shallow riffles than in the deeper water pools and stream edges. These
alternatives await evaluation by future research.
Introduction
The platypus Ornithorhynchus anatinus is a semi-aquatic
monotreme mammal confined largely to freshwater habitats
in eastern Australia. It feeds on benthic invertebrates by
sifting fine sediments, skimming the surface of large under-
water rocks and boulders with the bill and turning rocks
with the fore feet to access interstitial prey. It consumes a
wide variety of prey, mainly benthic insects at all life stages,
but also crustaceans (decapod shrimps and ostracods),
bivalve and gastropod molluscs, oligochaetes and gordian
worms (Faragher, Grant & Carrick, 1979; Grant, 1982).
Previous work has suggested that the platypus is a predomi-
nantly opportunistic predator of these aquatic invertebrates,
but also that Trichoptera are the most common constituent
of the diet in study areas in New South Wales and Tasmania
(Grant & Carrick, 1978; Faragher et al., 1979; Grant, 1982;
Bethge, 2002). Little is known about foraging habitat selec-
tion in the platypus as the few studies comparing diet and
prey availability have examined selectivity of invertebrates
from combined riffle and pool faunas (Faragher et al., 1979;
Grant, 1982). Furthermore, these studies identified prey
mainly to the relatively high taxonomic level of order, and
hence may not have detected finer-scale patterns of prey or
habitat selection.
Platypuses possess cheek pouches in which they store fresh
and partially processed macroinvertebrates that they have
collected from the stream benthos. The animals have a very
small stomach, so that the cheek pouches appear to partially
replace the stomach’s function as a food storage organ
(Harrop & Hume, 1980). Between foraging dives, when the
cheek pouches are full, platypuses rest on the water surface
and transfer the cheek pouch contents into the buccal cavity.
Here, they are masticated by the grinding of keratinized pads
on the maxillae and lower jaw (Harrop & Hume, 1980).
Unwanted items such as exoskeletons, caddisfly cases, sand
and other indigestible materials are thought to be ejected into
the water by filtering through serrations on the margin of the
lower jaw, and the remaining material is ingested.
Within streams there are three major habitats for macro-
invertebrates: lotic-erosional (running water riffles); lotic-
depositional (pools) and littoral margins or stream edges.
These habitats have distinctive macroinvertebrate assem-
blages adapted to the physical, hydrological and chemical
characteristics of each habitat (Wallace & Anderson, 1996).
Riffles are the shallow and rocky high-energy sections of
Journal of Zoology
Journal of Zoology 280 (2010) 237–246 c2009 The Authors. Journal compilation c2009 The Zoological Society of London 237
Journal of Zoology. Print ISSN 0952-8369
streams, characterized by coarse sediments and generally
steep gradients that produce turbulent water and fast flows.
Pools are the mid-stream sections with low to minimal flow,
usually deeper than riffles, and often with depositional areas
containing softer sediments such as sand or silt. Stream edges
are structurally complex, with overhanging vegetation, under-
cut banks, logs and coarse woody debris, with small back-
waters, eddies and often stands of submerged and emergent
aquatic plants. The depth can vary depending on the slope of
the stream bank (Humphries, Davies & Mulcahy, 1996).
The aims of this study were to characterize the diet of
platypuses in streams in south-eastern New South Wales,
Australia, and to examine whether diet reflects the availabil-
ity of prey within the river system. We evaluated evidence for
selection of particular taxa in specific habitats and across
seasons, as well as between the sexes. Male platypuses are
much larger than females (Grant & Temple-Smith, 1983;
McLachlan-Troup, 2007). Such dimorphism in size may
influence both diet and prey selection; this effect occurs often
in sexually dimorphic species (Shine et al., 1998; Lunney,
Matthews & Grigg, 2001) and may facilitate niche separation
between the sexes (Selander, 1966). Differential predation by
the sexes may in turn affect the structure of prey commu-
nities (Schmitz, 2005; Dickman & Murray, 2006).
Materials and methods
Study area
The study was centred at Kangaroo Valley (1501350S,
341440E), 160 km south of Sydney, in the southern Highlands
of New South Wales, Australia. The site forms a sub-
catchment of the Shoalhaven River, and rises from an
altitude of about 80–670 m in the headwater reaches. The
climate is mild, with cool winters and warm summers with
moderate rainfall that is generally highest in autumn and
winter. Two major waterways flow through Kangaroo Val-
ley: Kangaroo River and its main tributary, Brogers Creek.
Brogers Creek and Kangaroo River flow through steep-
sided valleys surrounded by pasture and dairy farms. The
streams are characterized by rocky-bottomed pool-riffle
sequences that are confined by bedrock, with pockets of
alluvium that form banks on which riparian vegetation
grows and where platypuses excavate their burrows. Ripar-
ian trees are dominated by river oak Casuarina cunning-
hamiana and eucalypts (Eucalyptus spp.), with an
understorey of sedges Lomandra longifolia, grasses and
herbs. In the undisturbed upper reaches, subtropical ripar-
ian vegetation occurs with tree ferns (Cyathea spp. and
Dicksonia antarctica) and palms Livistonia australis.
Diet
The diet of platypuses in Brogers Creek and the Kangaroo
River was determined by examination of cheek pouch
contents. We captured platypuses at various sites along both
watercourses between August 1998 and April 2000, gener-
ally at intervals of 5–6 weeks, using standard netting techni-
ques (Grant & Carrick, 1974). These involved setting
unweighted gill nets (7 cm mesh), usually in pools, from
about an hour before dusk until 00:00–03:30 h, and mon-
itoring them continuously. Platypuses were removed from
the nets within 10 min of capture, processed and then
released 20–30 min later.
For handling, platypuses were placed in pillowcases with
the corners cut off. This covered the animals’ eyes and
allowed their bills to protrude, providing a calming and
effective restraint. A specially constructed small, curved
spatula was used to scrape out the contents of both cheek
pouches, removing 50–98% of the cheek pouch material
(Faragher et al., 1979). Contents of both cheek pouches were
combined into a single sample per individual, preserved in
80% ethanol and then returned to the laboratory. Animals
were sexed and microchipped before release. The volume of
cheek pouch material was assessed before identification.
Samples were transferred to a test tube and the contents
allowed to settle for an hour; volumetric measurements were
then made to the nearest 0.1 mL. Only samples Z0.5 mL
were examined, as smaller samples were considered too small
to be representative of the diet. In total, 50 individual samples
Z0.5 mL were collected: eight from spring (September–No-
vember), 12 from summer (December–February), 12 from
autumn (March–May) and 18 from winter (June–August).
To identify prey types, cheek pouch material was spread
in a grooved sorting tray and examined under 8–40
magnification using a compound microscope. The material
was usually finely divided and contained many fragments of
insect cuticle and sand, but more intact items could be
identified to family by comparison with macroinvertebrates
collected from the streams and by reference to keys (Good-
erham & Tsyrlin, 2002). Due to difficulties in identification,
oligochaetes and amphipods were not classified to family.
As differential recognition of prey could bias the results
towards identification of distinctive taxa, we scored diet on a
presence/absence basis per cheek pouch sample and ex-
pressed prey taxa as percentage occurrence and percentage
frequency. Percentage occurrence provides a measure of the
relative importance of each prey type by calculating the
proportion of platypuses in which that prey is found
(number of cheek pouches nin which prey category coccurs,
n
c
, divided by the total number of cheek pouches examined
100). Percentage frequency expresses the relative impor-
tance of a particular prey item with reference to all items (n
c
divided by Sn
c
for all prey categories 100) (Sheil et al.,
1998; Benstead, Barnes & Pringle, 2001). We present per-
centage occurrence data in the body of the results but use the
frequency data to calculate Ivlev’s electivity index. We did
not attempt to calculate percentage volumes of different
prey types in the diet, as most items were comminuted too
finely to reconstruct for volumetric assessment.
Invertebrate sampling
The seasonal availability of macroinvertebrates was deter-
mined for both Brogers Creek and Kangaroo River over
10 months from May 1999 to February 2000. Six sites on
Journal of Zoology 280 (2010) 237–246 c2009 The Authors. Journal compilation c2009 The Zoological Society of London238
Diet and dietary selectivity of the platypus T. A. McLachlan-Troup, C. R. Dickman and T. R. Grant
both watercourses were selected on the basis of availability
of the three main habitats and ease of access. Each season,
we selected two of the six sites on each stream at random and
sampled all three habitats, thus yielding a combined total of
48 samples. All samples were collected by day. Although
platypuses forage mainly at night, they are also active to
some degree during daylight (Grant, 1983; Gust & Handa-
syde, 1995; Otley, Munks & Hindell, 1998), and inverte-
brates are available throughout the diel cycle.
Riffle samples were collected using a 350 mm mesh sweep net
(opening 33 26 cm) by holding the net opening downstream,
flush with the substratum, and walking backwards upstream
through the riffle, kicking and dislodging the substratum along
a 10 m transect. Dislodged invertebrates and other material
were washed into the net by the stream flow. We attempted to
obtain samples that were representative of the various flows
and depths in the riffles. Pool bottom samples were collected
using the same net and walking backwards through the pools,
kicking and shuffling the feet through the benthic substratum.
The net opening was swept backwards and forwards through
the material dislodged and suspended in the water column.
Again, we walked a 10 m transect to collect samples represen-
tative of the various depths and substrata in the pools. Edge
samples were collected by sweeping the same net vigorously
along pool margins and backwaters on stream edges, through
submerged vegetation, under overhanging banks (where pre-
sent) and through accumulations of detritus. This allowed
collection of representative samples from 10 m transects of
stream edge. Due to their rapid escape response and mobility,
freshwater crayfish may not have been sampled adequately,
although none was observed over the course of this research
despite many hours of wading, snorkelling and underwater
observations in the streams in all seasons.
Large sticks, leaves and stones were removed after in-
spection to ensure that no macroinvertebrates would be
discarded, then whole samples were preserved in 80%
ethanol and returned to the laboratory for processing.
Samples were hand sorted under 8–10 magnification,
macroinvertebrates were identified to family where possible,
and enumerated. Taxa with morphologically, behaviourally
or functionally distinct larval and adult stages, such as the
beetles Elmidae and Dytiscidae, were maintained as sepa-
rate taxonomic units in analyses. Sixty-five per cent of the
samples were whole-sorted but, to reduce sorting time of
bulky samples, 17 of the 48 samples collected (35%) were
sub-sampled to 25% of the sample volume. Macroinverte-
brate counts for these sub-samples were calculated as actual
count 4. We made no attempt to assess the availability of
fish, frogs or other vertebrates in the study area. Although
these prey types occur on occasion in the diet of platypuses
elsewhere (Faragher et al., 1979; Grant, 1982), we found no
vertebrate remains in pilot samples of cheek pouch material
from either Brogers Creek or Kangaroo River.
Data analysis
Comparisons were made between sex, season and taxon
richness of cheek pouch samples, and sex, season and
volume of the samples. Data were tested for normality and
homogeneity of variances (Underwood, 1997) and, where
required, transformed before analysis of variance (ANOVA)
using SYSTAT v9.A priori planned comparisons between
treatments were analysed with a Tukey HSD test. We also
correlated sample volume and number of taxa present in the
cheek pouch samples to determine any association.
To compare the overall composition of the diet in the
cheek pouch samples between sex and season and for
analyses comparing the invertebrates available between
sites, seasons and habitats, we used PRIMER v 5 (Clarke &
Warwick, 1994). The Bray–Curtis dissimilarity measure was
used to calculate association matrices before ordination
using non-metric multi-dimensional scaling (nMDS). Data
were transformed as required before analyses and used to
scale the original data to obtain a balance between common
and rarer taxa in similarity measures. The square-root
transformation moderately down-weights the effects of
common species, placing emphasis on these taxa while still
maintaining the influence of moderately abundant species
(Clarke & Warwick, 1994). Presence/absence transforma-
tions of the invertebrate availability data were required for
comparisons with the dietary data. Following nMDS, we
used ANOSIM (analysis of similarity) to detect differences
between groups, then SIMPER (similarity percentages)
analysis to identify taxa contributing to average dissimilar-
ity between macroinvertebrates in the diet of platypuses and
in the three habitats studied (see Glen & Dickman, 2006).
Ivlev’s electivity index ({% frequency of items in the
diet% available in the environment} divided by {%
frequency in the diet+% available in the environment})
(Ivlev, 1961) was used to identify any differential selectivity
for invertebrate prey in the different habitats studied. It is
widely used (Collier, 1991), and sensitive to the relative
densities of available dietary items (Krebs, 1989). Ivlev’s
index was calculated from the percentage frequencies of
invertebrates in the diets of platypuses and in sweep net
samples in each habitat and season to determine the degree
and direction of selection. Values range from +1 (selection
for, or greater accessibility of, a particular prey item) to 1
(avoidance, or inaccessibility of, that item); zero indicates no
selection. We display data as percentage summaries of all
taxa selected by platypuses by habitat and season.
Results
Diet
The cheek pouch material was diverse, with 55 macroinver-
tebrate families from 16 orders identified. Overall,
12.2 1.0 SE families were found per cheek pouch sample,
with families within Trichoptera and psephenid beetles
being encountered most commonly (Table 1). Other animal
taxa in the cheek pouches included two individual terrestrial
ants and a terrestrial weevil, most likely collected inadver-
tently by platypuses and some platypus guard hairs, pre-
sumably from grooming. No vertebrate remains were found.
There were no differences in cheek pouch sample volumes
Journal of Zoology 280 (2010) 237–246 c2009 The Authors. Journal compilation c2009 The Zoological Society of London 239
Diet and dietary selectivity of the platypusT. A. McLachlan-Troup, C. R. Dickman and T. R. Grant
(mL) between male (mean = 1.33 0.13 SE) and female
platypuses (mean= 1.28 0.13 SE), nor between seasons
(spring =1.33 0.13 SE, summer =1.50 0.20 SE, autumn
= 1.70 0.23 SE, winter =1.42 0.24 SE); there was no sex -
season interaction (Table 2).
There was no difference overall in invertebrate taxon
richness (number of taxa) in the cheek pouch samples of
male and female platypuses (Table 3, Fig. 1a). However,
invertebrate richness differed between seasons, with richness
in summer exceeding that in winter (Tukey’s HSD,
Po0.05); there was no sex season interaction (Table 3,
Fig. 1b).
Cheek pouch sample volume and number of taxa were
correlated (r=0.327, P= 0.021) indicating that larger sam-
ples contained a greater range of prey types.
There was no difference overall in the composition of
dietary items between the sexes (ANOSIM, n= 48, global
R=0.033, P=0.08), with the nMDS ordination showing
considerable spread and overlap of sample points (Fig. 2).
Dietary composition differed between summer and winter
(ANOSIM, n=48, global R= 0.017, P= 0.015; Fig. 3), but
not between any other seasons. The stonefly family, Gripop-
teryigidae, provided the greatest contribution to this differ-
ence, followed by adult elmid beetles, worms and
chironomid fly larvae (Table 4).
Availability of invertebrates
The assemblage of aquatic macroinvertebrates was extre-
mely diverse, comprising adult and larval insects, molluscs,
crustaceans, worms, water mites and other invertebrate
taxa. We identified 74 families from 16 orders in the habitat
samples, including representatives of all taxa found in the
cheek pouch samples of platypuses.
In pools, Ephemeroptera were found most commonly
across all seasons, followed by Diptera and Trichoptera. In
riffles, Trichoptera appeared most frequently, then Ephe-
meroptera and Diptera. On stream edges, Trichoptera and
Ephemeroptera were numerically dominant and about
equivalent, except in summer when numbers of Trichoptera
exceeded those of Ephemeroptera.
In multivariate comparisons, invertebrate assemblage
structure did not vary between seasons (ANOSIM, n= 48,
Table 1 Macroinvertebrate taxa found most frequently in cheek
pouch samples from platypuses Ornithorhynchus anatinus,ex-
pressed as % occurrence (n= 50 samples)
Order Family
Percentage
occurrence
Trichoptera Leptoceridae 90
Coleoptera Psephenidae 90
Ephemeroptera Leptophlebiadae 50
Trichoptera Helicopsychidae 46
Annelida Oligochaeta 40
Trichoptera Odontoceridae 40
Megaloptera Corydalidae 40
Mollusca Planorbidae/Physidae 40
Odonata Gomphidae 34
Plecoptera Gripopteryigidae 34
Table 2 Two-factor ANOVA on volumes of cheek pouch samples
from platypuses Ornithorhynchus anatinus, comparing sex by season
(root-transformed, n=50)
Source d.f. Mean-square F-ratio P
Sex 1 0.007 0.102 0.751
Season 3 0.074 1.036 0.387
Sex season 3 0.101 1.409 0.254
Error 42 0.072
Table 3 Two-factor ANOVA on invertebrate taxon richness in the diet
of platypuses Ornithorhynchus anatinus, comparing sex by season
(root-transformed, n=50)
Source d.f. Mean-square F-ratio P
Sex 1 0.648 1.547 0.220
Season 3 1.800 4.299 0.010
Sex season 3 0.793 1.894 0.145
Error 42 0.419
(b)
Female Male
0
5
10
Richness
Richness
15
20
Sex
Autumn
Spring
Summer
Winter
0
5
10
15
20
25
Season
(a)
Figure 1 Mean taxon richness in cheek pouch
samples from platypuses Ornithorhynchus ana-
tinus (number of families SE), shown for (a)
the two sexes; (b) seasons.
Journal of Zoology 280 (2010) 237–246 c2009 The Authors. Journal compilation c2009 The Zoological Society of London240
Diet and dietary selectivity of the platypus T. A. McLachlan-Troup, C. R. Dickman and T. R. Grant
global R=0.017, P=0.25, Fig. 4), or in any pair-wise
season by season comparison. However, assemblage com-
position varied markedly between habitats (ANOSIM,
n=48, global R= 0.239, P= 0.001), with no overlap ap-
parent between the riffles and other habitats (Fig. 5). Pools
and edges overlapped somewhat in ordination space, but
still differed significantly from each other.
The 10 taxa contributing most to the observed differences
in macroinvertebrate assemblages between stream habitats
are presented as pair-wise SIMPER analyses in Table 5. In
the pool and riffle comparison (Table 5A) trichopteran
families were most strongly represented, whereas in the pool
versus edge comparison (Table 5B), molluscs, notonectid
bugs and several coleopteran families contributed most to
the differences in composition. Trichopteran families con-
tributed most to the compositional differences in macro-
invertebrates between edges and riffles, followed by
Odonata (Table 5C).
Comparison of the diet of platypuses with
available invertebrates
The richness of invertebrates in the diet of platypuses was
usually less than that sampled in the three stream habitats
Figure 2 Non-metric multi-dimensional scaling (nMDS) of invertebrate
taxa in cheek pouch samples from male and female platypuses
Ornithorhynchus anatinus. Bray–Curtis dissimilarity, presence/ab-
sence transformation (m, male platypuses; &, female platypuses)
(stress=0.19).
Figure 3 Non-metric multi-dimensional scaling (nMDS) of invertebrate
taxa in cheek pouch samples from platypuses Ornithorhynchus
anatinus in four seasons. Bray–Curtis dissimilarity, fourth root trans-
formation (m, spring; ,, summer; &, autumn; ~, winter)
(stress=0.19).
Table 4 Macroinvertebrate families contributing most to the ob-
served difference in composition between cheek pouch samples
from platypuses in summer and winter (SIMPER analysis)
Order Family % contribution
Plecoptera Gripopterygidae 4.56
Coleoptera Elmidae (A) 4.45
Oligochaeta Oligochaeta 4.24
Diptera Chironomidae (L) 3.95
Coleoptera Dytsicidae (A) 3.84
Trichoptera Helicophidae 3.76
Ephemeroptera Caenidae 3.69
Coleoptera Dytiscidae (L) 3.56
Trichoptera Helicopsychidae 3.53
Odonata Gomphidae 3.47
A, adult; L, larvae.
Figure 4 Non-metric multi-dimensional scaling (nMDS) of stream
invertebrate taxa sampled in four seasons. Bray–Curtis dissimilarity,
fourth root transformation (m, spring; &, summer; , autumn; ~,
winter) (stress=0.19).
Journal of Zoology 280 (2010) 237–246 c2009 The Authors. Journal compilation c2009 The Zoological Society of London 241
Diet and dietary selectivity of the platypusT. A. McLachlan-Troup, C. R. Dickman and T. R. Grant
across all seasons. Summer was the only exception, when the
richness of invertebrates only in the edge and riffle habitats
differed from that in the diet (Tukey’s HSD, Po0.05, Table
6, Fig. 6a and d).
The composition of invertebrates in the diet of platypuses
was markedly different in ordination space from that in each
of the three stream habitats (Fig. 7), probably due to the
lower family-level richness of invertebrates in the diet
compared with that in the stream habitats. However, some
caution is warranted in interpreting the ordination due to
the high stress value (0.23). The taxa consumed by platy-
puses were also represented in all habitats, but not equally
so (Table 7). Platypuses generally showed strongest selection
for invertebrates in edge habitats, followed by those in
pools. Riffles exhibited consistently fewer and lower positive
selection coefficients compared with pools and edges, sug-
gesting that this habitat was not as frequently foraged as the
other two habitats.
Discussion
Platypuses in Kangaroo Valley consumed a wide variety of
aquatic invertebrates. Only three terrestrial invertebrates
were found in cheek pouch samples among 55 aquatic
macroinvertebrate families from 16 orders, demonstrating
the importance of aquatic prey. Despite this, platypuses did
not eat all prey types that were potentially available, as a
further 19 families of invertebrates were found in the
streams where platypuses were studied. Occurrence of a
restricted range of prey items in the cheek pouch samples of
individual platypuses (mean of 12.2 macroinvertebrate fa-
milies per sample) is not unexpected and may reflect how
long and where an individual has been foraging before
capture as well as the unknown period over which items are
stored in the cheek pouches. However, the disparity between
the 55 invertebrate families in the diet and the 74 sampled
from the three habitats suggests that platypuses were fora-
ging selectively. We were able to examine the diet of
platypuses at a finer level of taxonomic resolution than in
previous studies (Faragher et al., 1979; Grant, 1982), thus
allowing patterns of selection to be identified. As different
families in the same order may occupy different functional
niches (e.g. Trichoptera contains detritivorous, herbivorous
Figure 5 Non-metric multi-dimensional scaling (nMDS) of invertebrate
taxa sampled from three stream habitats. Bray–Curtis dissimilarity,
fourth root transformation (, pool; &, riffle; m, edge) (stress = 0.19).
Table 5 Macroinvertebrate taxa contributing most to the observed
difference in composition between stream habitats (pair-wise SIM-
PER analyses between habitats)
Order Family % contribution
(A) Pool versus riffle
Trichoptera Hydropsychidae 4.4
Trichoptera Hydrobiosidae 4.4
Diptera Tipulidae 3.92
Megaloptera Corydalidae 3.81
Trichoptera Philopotamidae 3.79
Trichoptera Glossosomatidae 3.55
Odonata Telephlebiadae 3.39
Ephemeroptera Caenidae 3.15
Trichoptera Helicophidae 2.93
Decapoda Atyidae 2.87
(B) Pool versus edge
Mollusca Planorbidae/Physidae 4.70
Hemiptera Notonectidae 3.84
Coleoptera Elmidae 3.63
Coleoptera Scirtidae 3.49
Ephemeroptera Caenidae 3.10
Trichoptera Helicopsychidae 3.07
Odonata Gomphidae 3.04
Diptera Ceratopogonidae 2.99
Coleoptera Dytiscidae 2.97
Mollusca (bivalve) Sphaeridae 2.92
(C) Edge versus riffle
Trichoptera Hydrobiosidae 3.75
Odonata Corydalidae 3.55
Trichoptera Glossosomatidae 3.52
Trichoptera Philopotamidae 3.3
Trichoptera Hydropsychidae 3.26
Coleoptera Elmidae 3.11
Odonata Telephlebiadae 2.94
Diptera Tipulidae 2.93
Mollusca Planorbidae/Physidae 2.75
Hemiptera Notonectidae 2.66
Table 6 One factor ANOVAs on invertebrate taxon richness (number
of families) in the diet of platypuses Ornithorhynchus anatinus and in
three stream habitats across four seasons, based on data shown in
Fig. 6
Season d.f. Mean-square F-ratio P
Spring 3 2.964 12.361 o0.001
Summer 3 3.056 7.427 0.002
Autumn 3 4.748 16.012 o0.001
Winter 3 8.756 19.090 o0.001
Journal of Zoology 280 (2010) 237–246 c2009 The Authors. Journal compilation c2009 The Zoological Society of London242
Diet and dietary selectivity of the platypus T. A. McLachlan-Troup, C. R. Dickman and T. R. Grant
and predatory families; Gooderham & Tsyrlin, 2002), de-
tailed identification of prey also allows food webs to be
constructed and forager impacts to be specified (McLa-
chlan-Troup, 2007). It is also possible that bill electrorecep-
tion may play a role in the dietary selectivity reported in this
study. Electromyogenic potentials of typical platypus prey
items vary between species, with most being outside the
range of potentials known to be detected by the platypus
(Taylor et al., 1992). Although electroreception is thought to
be involved in sophisticated prey detection (Pettigrew,
Manger & Fine, 1998), mechanoreceptor in the bill may also
be involved and the exact nature of the use of these two well-
developed senses in foraging by the species is not yet clearly
evaluated (Proske & Gregory, 2003, 2004). Recent studies of
0
10
20
30
40
Winter
0
10
20
30
40
Autumn
Diet Edge Pool Riffle Diet Edge Pool Riffle
Diet Edge Pool Riffle Diet Edge Pool Riffle
0
10
20
30
40 (a) (b)
(c) (d)
Spring
0
10
20
30
40
Summer
Richness
Richness
Richness
Richness
Figure 6 Seasonal comparisons of invertebrate
taxon richness in the diet of platypuses and
from three stream habitats. Means are
shown SE. (a) Spring; (b) summer; (c) autumn;
(d) winter.
Figure 7 Non-metric multi-dimensional scaling (nMDS) of invertebrate
taxa sampled from cheek pouches of platypuses Ornithorhynchus
anatinus and from three stream habitats. Bray–Curtis dissimilarity,
presence/absence transformation (m, pool; , riffle; &, edge; ~,
cheek pouch sample) (stress=0.23).
Table 7 Summary table showing percentages of taxa present in both
the diet of platypuses Ornithorhynchus anatinus and in each of three
stream habitats that are positively selected by platypuses, using
Ivlev’s index of electivity
Season Habitat % positive selection
Spring Pool 65.0
Riffle 62.5
Edge 76.2
Summer Pool 67.7
Riffle 60.0
Edge 85.3
Autumn Pool 75.0
Riffle 62.5
Edge 79.0
Winter Pool 76.0
Riffle 66.7
Edge 82.1
Journal of Zoology 280 (2010) 237–246 c2009 The Authors. Journal compilation c2009 The Zoological Society of London 243
Diet and dietary selectivity of the platypusT. A. McLachlan-Troup, C. R. Dickman and T. R. Grant
platypus DNA sequences indicate significant genetic repre-
sentation of olfactory receptors, particularly those asso-
ciated with the vomeronasal system (Grus, Shi & Zhang,
2007), suggesting that foraging in the platypus may be even
more sophisticated, possibly also involving olfaction.
We found no differences in the diet of male and female
platypuses in terms of overall taxon richness. Although this
is the first study to examine dietary differences between sexes
in the platypus, this finding was unexpected as other
mammals that show strong sexual dimorphism in size often
differ in diet (Clutton-Brock, Iason & Guiness, 1987; Weir,
Harestad & Wright, 2005) or foraging behaviour (Dickman,
1986; Stokke, 1999). In this study, male platypuses were
35% larger than females (McLachlan-Troup, 2007), which
might suggest that they should differ in the amount, or
types, of food taken. It is possible that this size difference is
not enough to result in a detectable difference in taxa
represented in the diet, as is found in cervids (Perez-Barberia
& Gordon, 1998; Weir et al., 2005), or that any differences
were masked due to the difficulty of identifying masticated
prey remains.
Diets differed seasonally, with winter and summer being
most dissimilar. As there was no detectable change in the
composition of invertebrate assemblages with season, it is
unlikely that platypus diets reflected seasonal changes in
prey availability. A lack of seasonality in invertebrate
assemblages has been reported in other southern hemisphere
waters (Hart, 1985) and here may reflect the climatic
unpredictability of eastern Australian streams (Bunn, Ed-
ward & Loneragan, 1986). Given the evident lack of change
in the composition of available prey, it is most likely that
shifts occurred in dietary selection within the Kangaroo
Valley platypus population between seasons. This could
reflect seasonal changes in the energy contents of prey
(Cummins & Wuycheck, 1971) or in animals’ metabolic
demands and/or thermal stresses (Grant & Dawson, 1978;
Fanning & Dawson, 1980). In captivity, female platypuses
show dramatic increases in food consumption during lacta-
tion in summer (Holland & Jackson, 2002); despite the lack
of a significant sex season interaction here, this may result
in females taking a broader range of prey. Females may also
eat more invertebrates overall during summer without
necessarily selecting some prey types over others. Our use
of only presence/absence data meant that we could not have
detected such increased consumption.
Platypuses foraged in all stream habitats, but not equally
so, suggesting that prey was taken selectively within the river
system. Animals generally showed stronger selection for
invertebrates from stream edge habitats, closely followed
by pools and then, more distantly, riffles. Several reasons
may account for these patterns. Firstly, while many inverte-
brates occur in riffles (Fig. 6), relatively fewer of them may
be suitable prey for platypuses. Many riffle invertebrates
attach firmly to the substratum and are difficult to dislodge;
if they are prised off, there may be increased risks of them
being washed quickly downstream in the fast-flowing water.
Secondly, riffle substrata in our stream system were com-
posed of cobbles, boulders and coarse pebbles that may be
too large for platypuses to move, hence making effective
foraging difficult. Thirdly, foraging in high velocity waters
has energetic costs associated with buoyancy, endurance
and swimming ability (Bethge, 2002). As for other semi-
aquatic mammals (Williams, 1998), the hydrologically tur-
bulent riffle habitat may be too physiologically challenging
for platypuses to exploit regularly, although our observa-
tions showed that animals did forage occasionally in riffles.
Faragher et al. (1979) also suggested that platypuses
exploited riffles for foraging in the upper Shoalhaven river
in New South Wales. These authors reported the occurrence
(37% of cheek pouches) and a high selection coefficient for
beetle larvae of the family Psephenidae, while finding few of
these prey in pool and drift samples but high numbers in
riffles. Fourthly, shallow riffle areas may expose foraging
platypuses to predators (Serena, 1994; Grant, 2007); they
may thus be used for passage between pools but avoided as
feeding areas. Animals often avoid predation by foraging in
areas with lower predation risk, even if their energetic or
nutritional returns are reduced (Ekl ¨
ov & Halvarsson, 2000;
Chambers & Dickman, 2002). Fifthly, as platypuses were
captured mostly in nets set in pools, it is possible that our
samples were skewed by animals that had been foraging in
this habitat; sampling from animals captured in riffles would
be needed to test this. However, such bias is unlikely to be
strong. Pools and riffles were usually close together so our
placement of nets should not have precluded riffle-foraging
animals from being caught. Platypuses also showed stron-
gest selection for edge habitats where nets were seldom set.
Selection of stream edges over pools is particularly interest-
ing. Edges are more likely than open pools to expose
foraging platypuses to risk of predation by terrestrial
carnivores such as foxes or dogs (Serena, 1994; Grant,
2007). However, stream banks associated most commonly
with the occurrence of platypuses are often vertical or
undercut and have low overhanging riparian vegetation,
which may reduce exposure to these predators (Serena et al.,
1998, 2001; Grant, 2004).
Finally, dietary selectivity could reflect predator avoid-
ance by prey, mediated by responses to predator odour or
activity in the shallow riffles rather than in the deeper water
habitats. Such responses are well recognized in aquatic
predator–prey systems (McIntosh & Peckarsky, 1996; Chi-
vers et al., 2001), and can considerably reduce the impacts of
direct predation. There is no evidence that platypuses have
such an effect on their prey, but it remains a distinct and
intriguing area for future research.
Acknowledgements
Funding was provided through an Australian Postgraduate
Award and the Linnean Society of NSW. Mesh nets were
licensed by NSW Fisheries (permit no. F98/211), platypus
capturing and handling procedures were licensed by the
NSW National Parks and Wildlife Service, now Department
of Environment, Climate Change and Water (permit no.
B1874), and all platypus handling methods were authorized
Journal of Zoology 280 (2010) 237–246 c2009 The Authors. Journal compilation c2009 The Zoological Society of London244
Diet and dietary selectivity of the platypus T. A. McLachlan-Troup, C. R. Dickman and T. R. Grant
by the University of Sydney Animal Ethics Committee
(permit no. L04/6-98/3/2780).
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Diet and dietary selectivity of the platypus T. A. McLachlan-Troup, C. R. Dickman and T. R. Grant
... www.nature.com/scientificreports/ Platypuses prey on a wide variety of benthic macroinvertebrates such as insects, crustaceans, worms, and molluscs, with the orders of Trichoptera, Ephemeroptera, Odonata, and Coleoptera most commonly consumed 25,[27][28][29][30] . Their diet has been shown to vary seasonally in the wild 25,28 and captivity 31,32 , with no reported differences between males and females. ...
... Platypuses prey on a wide variety of benthic macroinvertebrates such as insects, crustaceans, worms, and molluscs, with the orders of Trichoptera, Ephemeroptera, Odonata, and Coleoptera most commonly consumed 25,[27][28][29][30] . Their diet has been shown to vary seasonally in the wild 25,28 and captivity 31,32 , with no reported differences between males and females. ...
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... Research into platypus diets is mostly based on sampling the contents of cheek pouches (Grant and Carrick 1978;Faragher et al. 1979;McLachlan-Troup et al. 2010;Marchant and Grant 2015) or analysis of captive nutrition (Thomas et al. 2018b), with more recent application of stable isotope analysis of platypus fur indicating that a combination of cheek pouch and stable isotope analyses is the most thorough approach . Feeding behavior of captive platypuses indicates that preferences are shaped by prey mobility and increased energy consumption associated with preparing for and recovering from breeding (Thomas et al. 2018b). ...
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The platypus (Ornithorhynchus anatinus) is one of the world's most evolutionarily distinct mammals, one of five extant species of egg-laying mammals, and the only living species within the family Ornithorhynchidae. Modern platypuses are endemic to eastern mainland Australia, Tasmania, and adjacent King Island, with a small introduced population on Kangaroo Island, South Australia, and are widely distributed in permanent river systems from tropical to alpine environments. Accumulating knowledge and technological advancements have provided insights into many aspects of its evolutionary history and biology but have also raised concern about significant knowledge gaps surrounding distribution, population sizes, and trends. The platypus' distribution coincides with many of Australia's major threatening processes, including highly regulated and disrupted rivers, intensive habitat destruction, and fragmentation, and they were extensively hunted for their fur until the early 20th century. Emerging evidence of local population declines and extinctions identifies that ecological thresholds have been crossed in some populations and, if threats are not addressed, the species will continue to decline. In 2016, the IUCN Red Listing for the platypus was elevated to "Near Threatened," but the platypus remains unlisted on threatened species schedules of any Australian state, apart from South Australia, or nationally. In this synthesis, we review the evolutionary history, genetics, biology, and ecology of this extraordinary mammal and highlight prevailing threats. We also outline future research directions and challenges that need to be met to help conserve the species.
... Climatic influence on breeding seasons can be seen across their range also, with courtship followed by nesting behaviour beginning in August in New South Wales while in Tasmania it is starts in October [64][65][66] . Habitats also vary across the platypuses' range, with differences in their food of aquatic macroinvertebrates [67][68][69][70][71] . Platypus habitat quality and health are under increasing pressure from anthropogenically driven stressors, including water resource development lowering water availability and altering the natural flow regime, land clearing destroying riparian vegetation, bank erosion and sedimentation, as well as pollution, all of which vary in largely unquantified severity across their range [72][73][74][75][76][77][78] . ...
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Platypuses ( Ornithorhynchus anatinus ) inhabit the permanent rivers and creeks of eastern Australia, from north Queensland to Tasmania, but are experiencing multiple and synergistic anthropogenic threats. Baseline information of health is vital for effective monitoring of populations but is currently sparse for mainland platypuses. Focusing on seven hematology and serum chemistry metrics as indicators of health and nutrition (packed cell volume (PCV), total protein (TP), albumin, globulin, urea, creatinine, and triglycerides), we investigated their variation across the species’ range and across seasons. We analyzed 249 unique samples collected from platypuses in three river catchments in New South Wales and Victoria. Health metrics significantly varied across the populations’ range, with platypuses from the most northerly catchment, having lower PCV, and concentrations of albumin and triglycerides and higher levels of globulin, potentially reflecting geographic variation or thermal stress. The Snowy River showed significant seasonal patterns which varied between the sexes and coincided with differential reproductive stressors. Male creatinine and triglyceride levels were significantly lower than females, suggesting that reproduction is energetically more taxing on males. Age specific differences were also found, with juvenile PCV and TP levels significantly lower than adults. Additionally, the commonly used body condition index (tail volume index) was only negatively correlated with urea, and triglyceride levels. A meta-analysis of available literature revealed a significant latitudinal relationship with PCV, TP, albumin, and triglycerides but this was confounded by variation in sampling times and restraint methods. We expand understanding of mainland platypuses, providing reference intervals for PCV and six blood chemistry, while highlighting the importance of considering seasonal variation, to guide future assessments of individual and population condition.
... Animals feed exclusively in the water on insects and other macroinvertebrates (e.g. McLachlan-Troup et al. 2010;Marchant and Grant 2015), most typically scanning for prey by rhythmically swinging the bill back and forth through a lateral arc while swimming near the channel bottom (Manger and Pettigrew 1995). Foraging preferentially occurs at a depth of around 1-3 m in lakes and rivers, though sometimes to a depth of nearly 9 m (Bethge et al. 2003;Grant 2004). ...
Article
The platypus’s tapered shape and benthic foraging habits predispose it to becoming entangled in encircling rings or loops of plastic, rubber or metal rubbish. Based on 54 cases of litter entanglement recorded in Victorian live-trapping surveys, items may encircle the neck (68%), torso (8%), jaw (2%) or be wrapped bandolier-fashion from in front of a shoulder to behind the opposite foreleg (22%). Entanglement frequency was eight times higher in the greater Melbourne region than in regional Victoria, and was significantly greater in first-year juveniles than in older animals and also in adult/subadult females compared with adult/subadult males. Items recovered from carcasses or from rescued animals that were unlikely to have survived without human intervention included elastic hair-ties, fishing line, a hospital identification wristband, an engine gasket and a plastic ring seal from a food jar; all of these items had cut through skin and (in most cases) deeply into underlying tissue. Up to 1.5% of the platypus residing in the greater Melbourne area and 0.5% of those living in regional Victoria are estimated to be at risk of entanglement-related injuries or death at any point in time.
... They are the only living representative of Ornithorhynchidae and one of only five species of mammals that lay eggs (Grant & Fanning, 2007). Platypuses primarily inhabit pools and riffles of rivers (<1-5 m), where a high complexity of bed substrates and stable riparian vegetation increases foraging opportunities (Grant & Fanning, 2007) for their primary prey of benthic invertebrates (McLachlan-Troup et al., 2010;Marchant & Grant, 2015;Klamt et al., 2016). Platypuses are elusive, being primarily nocturnal, and recapture rates are low (Grant, 2004), making abundances difficult to determine and resulting in few estimates of survival and population viability (Bino, Grant & Kingsford, 2015). ...
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• River regulation has extensively changed the ecology and hydrology of rivers worldwide, particularly downstream of dams, affecting the viability of freshwater species. The platypus (Ornithorhynchus anatinus) is a semiaquatic monotreme, endemic to eastern Australia, with a distribution overlapping Australia’s most regulated rivers. • Dams and changes to flow regimes have affected critical platypus habitat, yet our understanding of the impacts of these threatening processes on platypus ecology remains poor. Over a period of 3 years (2016–2018), platypuses were surveyed across three regions (Upper Murray, Snowy, and Border river regions), above and below large dams, and in adjacent unregulated rivers, comparing captures, demographics, abundances, and densities. We hypothesized that platypus captures and abundances would be lower downstream of dams, owing to altered flow regimes that have secondary impacts on the demographics of these populations. • In the Upper Murray Rivers region, captures were significantly lower in the Mitta Mitta River below Dartmouth Dam, compared with captures upstream of the dam and the unregulated Ovens River, probably reflecting significant alteration to the seasonality and temperature of flows caused by the dam. Conversely, there were no significant differences in captures or abundance and density estimates above and below the dams in the Snowy or Border river regions, where the extent of regulation was less severe, probably as a result of restoration efforts in recent years on some rivers. • Low proportions of juveniles on the Snowy River and Mitta Mitta River downstream of the dams, compared with upstream, raises concerns of other impacts of altered flow regimes to platypus breeding success and juvenile survival, given the sensitivity of juveniles to unseasonably high flows. • The results highlighted the potential impact of river regulation, with direct implications for the management of regulated rivers, providing opportunities to mitigate impacts through improved management of the seasonality and temperature of flows, to the benefit of platypuses and other freshwater species.
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Egg-laying mammals (monotremes) are a sister clade of therians (placental mammals and marsupials) and a key clade to understand mammalian evolution. They are classified into platypus and echidna, which exhibit distinct ecological features such as habitats and diet. Chemosensory genes, which encode sensory receptors for taste and smell, are believed to adapt to the individual habitats and diet of each mammal. In this study, we focused on the molecular evolution of bitter taste receptors (TAS2Rs) in monotremes. The sense of bitter taste is important to detect potentially harmful substances. We comprehensively surveyed agonists of all TAS2Rs in platypus (Ornithorhynchus anatinus) and short-beaked echidna (Tachyglossus aculeatus) and compared their functions with orthologous TAS2Rs of marsupial and placental mammals (i.e., therians). As results, the agonist screening revealed that the deorphanized monotreme receptors were functionally diversified. Platypus TAS2Rs had broader receptive ranges of agonists than those of echidna TAS2Rs. While platypus consumes a variety of aquatic invertebrates, echidna mainly consumes subterranean social insects (ants and termites) as well as other invertebrates. This result indicates that receptive ranges of TAS2Rs could be associated with feeding habits in monotremes. Furthermore, some orthologous receptors in monotremes and therians responded to β-glucosides, which are feeding deterrents in plants and insects. These results suggest that the ability to detect β-glucosides and other substances might be shared and ancestral among mammals.
Article
Globally, urban expansion and climate change interact to threaten stream ecosystems and are accelerating the loss of aquatic biodiversity. Waterway managers urgently need tools to understand the potential combined impacts of urbanisation and climate change, and to identify effective mitigating management interventions for protecting freshwater biota. We address this challenge using the semi-aquatic mammal the platypus (Ornithorhynchus anatinus) as a focal species. We developed high-resolution environmental spatial data for stream networks and spatially-explicit habitat suitability models to explore the impact of threats, and to identify the combination of management actions most likely to maintain or improve habitat suitability over the next 50 years in greater Melbourne, Australia. We developed and evaluated platypus habitat suitability models (males-and-females and females-only) including validation using an independent environmental DNA (eDNA) dataset. Platypus occurred more commonly in larger, cooler streams with greater catchment-weighted discharge, following periods of greater stream flow. They were positively associated with near-stream forest cover and negatively associated with annual air temperature and urban stormwater runoff. Extensive reductions in suitable platypus habitat are predicted to occur under urbanisation and climate change scenarios, with the greatest threat expected from reduced streamflows. This emphasises the importance of maintaining flow regimes as part of conserving platypus in the region, however, substantial additional benefit is predicted by concurrent riparian revegetation and urban stormwater management efforts (that also have the potential to contribute to the streamflow objectives). Provision of adequate streamflows in a future with increasing water demands and water security requirements will likely require creative integrated water management (IWM) solutions. Our high-resolution stream network and habitat suitability models have allowed predictions of potential range-shifts due to urban expansion and climate change impacts at management-relevant scales and at the whole-of-landscape scale. This has enabled systematic strategic planning, priority action planning and target setting in strategic policy development.
Article
The strong inter-dependence between terrestrial and freshwater ecosystems, mediated by the character of vegetation and landscapes, can have significant impacts to freshwater species. A changing climate towards hotter and drier climates is already increasing fire frequencies and severity around the world. The platypus (Ornithorhynchus anatinus) is an iconic freshwater Australia species, facing increasing threats since European colonisation and with a distribution which coincides with fire prone areas. While some evidence suggest platypuses are resilience to fires, the combination of severe bushfires and reduced water availability may have a significant effect to platypus populations. In this short communication we investigated the effects of fire on platypus populations in two rivers, following an extreme drought, comparing burnt and unburnt in adjacent river catchments, with similar habitat and geomorphology. Findings suggests significantly low platypus numbers in burned sites compared to those on the unburnt river, as well as to known densities across the species' range. Whether the fires directly impacted platypuses remains undetermined but the timing of the fires as well as an extreme drought likely impacted recruitment as we did not record any juveniles on both rivers. Platypuses are increasingly under threat from direct and indirect human developments across much of their range and increased frequency and severity of fires and droughts will further strain the viability of platypus populations, particularly in small streams more likely to dry out. Improving the resilience of platypus populations and their freshwater environments to both droughts and fires needs to become a priority.
Thesis
The aim of this study was to understand the distribution and genetic structure of platypus populations in Australia, and in particular to investigate the interactions of distribution and genetic structure. The research considered the entire distributional range of the platypus, but with a special focus on the scientifically neglected platypus populations of northern Queensland. Platypuses in north Queensland are smaller than their southern counterparts and have a more reddish colouration. There appears also to be a break in the distribution of the platypus between about Mackay and Townsville, which corresponds to the catchment of the Burdekin River and which geographically separates northern platypuses from southern populations. The relationship of northern and southern platypus populations of mainland Australia, together with the biogeographic significance to the platypus of the Burdekin break, was a binding thread throughout the study. However, before that relationship could be inferred there were several smaller gaps in the knowledge regarding the distribution of platypus that had to be filled. These gaps were represented by several intriguing questions: Where do platypuses occur and why is their distribution limited to those areas? And, how are local populations of platypuses structured and how do they relate to each other? With these key pieces of information it was possible to expand the scope of the study to a distribution-wide level. Using distribution modelling software (MaxEnt), climate data and 4,315 occurrence records, I produced a climate-based distribution model to describe the current distribution of the platypus. The two most important climate factors determining environmental suitability for the platypus were precipitation during the driest quarter (which was positively associated with platypus occurrence) and maximum temperature (negatively associated), to the near exclusion of all other variables (53.8% and 41.2% contributions respectively). This distribution map supported the existence of a significant distribution break occurring in northern Queensland. Separate modelling of the northern and southern distributions revealed differences in the limiting factors in each part of the range. To the south, precipitation during the driest quarter and maximum temperature remained the two most important factors (76.2% and 18.9% contribution respectively). However, in the north additional environmental factors were important. These were temperature seasonality, precipitation during wettest quarter, minimum temperature, and precipitation seasonality, with respective contributions to habitat suitability of 34.7%, 22.6%, 19.2%, 16.7% and 3.5%. The initial species distribution model was projected onto palaeo-climate data representing the last glacial maximum (c. 22,000 years before present). This palaeo-model indicated that overall conditions were less favourable for the platypus at that time, and that the gap between the northern and southern portions of the distribution would have been even more pronounced, although there may have been connectivity between Tasmania and the mainland via the Bass land bridge. The platypus distribution was also projected forward to predict the effects of anthropogenic climate change. An aggregated mean across the complex models involved in this suggested a likely decline in range of approximately 15% by the year 2070 with best/worst case scenarios depicting an increase of 3.5% or a decrease of 65% respectively. The areas affected by these distributional changes were the marginal fringes surrounding the main areas of distribution. After developing a reliable set of 12 microsatellite DNA markers for the study it was possible to investigate population structure and dynamics from a molecular perspective. At the finer scale of investigation (comparisons within and between adjacent river systems), I showed that despite individual sample sites within a river systems having some genetic differentiation, they generally exhibited a strong isolation-by-distance pattern within the system (e.g. Hawkesbury-Nepean system: r = 0.7315, p = 0.02). Moreover, significant differentiation between systems as suggested by pairwise Fst, AMOVA and Bayesian population clustering techniques indicates that the physical separation of river basins does limit gene flow and is responsible for local population structuring. The detection of several first generation migrants (13 of 120 samples) also provided a genetic indication that platypuses must move between river basins, which would require overland movement to occur more often than previously thought. I also showed that a large dam inhibited within-river gene flow and could lead to increased differentiation between populations: the construction of the Nepean Dam has lead to higher differentiation occurring within a single river (above vs. below dam pairwise Fst = 0.07681) then occurring between two rivers at three times the distance and requiring an overland crossing (Wingecarribee River vs. Nepean River pairwise Fst = 0.05978). Genetic analysis across the entire platypus distribution revealed three evolutionarily significant units within the platypus distribution that are in strong consensus with the observations gathered from the distribution modelling. These represent the isolated Northern Region, the Southern Mainland Region, and Tasmania. Within these evolutionarily significant units six discrete population clusters were identified, which formed the basis of five proposed management units for the platypus (two clusters were combined due to the presence of active gene flow). Attempts to investigate population sub-clusters within these clusters were futile as genetic admixture between local river systems rendered their level of distinctiveness below that of discrete conservation units. Future conservation and management planners will have to keep in mind that not all platypuses are created equal; there are distinct groups that must be considered independently in order to maintain the genotypic and phenotypic features that currently exist across the species.
Article
The seasonal activity patterns and habitat usage of platypuses were examined in Lake Lea, a sub-alpine lake system in north western Tasmania. Activity data were collected by radio tracking individuals for one 24 hour period (in two 12 hour blocks) using a portable radio-receiver and 3-element Yagi antenna. In addition, the location of other individuals was recorded periodically during the 24 hour period. Information collected so far for ten individuals during late winter and mid spring will be presented. Preliminary analysis suggests that a high proportion of the population may be diurnally active. Out of five adult platypuses tracked during late winter, three were predominantly diurnally active and only two were nocturnal. Day-active individuals emerged from burrows between 0530 and 0700 and returned before 1930, thus foraging for at least 13.5 hours per day. Nocturnal individuals emerged between 1730 and 1900, foraged for approximately 12.5 hours and returned between 0600 and 0700. Mean dive times of three day-active individuals were between 29 and 34 seconds, with an intervening surface period of between 12 and 20 seconds. Maximum foraging area of three individuals were between 14 and 30 hectares (95% isopleth, Kernel analysis).
Book
Since it first became known to European scientists and naturalists in 1798, the platypus has been the subject of controversy, interest and absolute wonder. Found only in Australia, the platypus is a mammal that lays eggs but, like other mammals, it has fur and suckles its young on milk. Many early biologists who visited the British colonies in Australia, including Charles Darwin, went out of their way to observe this remarkable animal. In Australia today the species is considered to be an icon, but one that many Australians have never seen in the wild. This book presents established factual information about the platypus and examines the most recent research findings, along with some of the colourful history of the investigation of its biology. This completely updated edition covers its anatomy, distribution and abundance, breeding, production of venom, unique senses, ecology, ancestry and conservation. It includes a 'Frequently Asked Questions' section for the general reader and, for those wishing to find out more detailed information, a comprehensive reference list.
Book
Freshwater macroinvertebrates provide a useful and reliable indicator of the health of our rivers, streams, ponds and wetlands. As environmental awareness within the community increases, there is an increasing interest in the need to assess the health of our local waterways and school curriculums are changing to reflect this important ecological trend. The Waterbug Book provides a comprehensive and accurate identification guide for both professionals and non-professionals. It contains an easy-to-use key to all the macroinvertebrate groups and, for the first time, high quality colour photographs of live specimens. It provides a wealth of basic information on the biology of macroinvertebrates, and describes the SIGNAL method for assessing river health. The Waterbug Book is full of practical tips about where to find various animals, and what their presence can tell about their environment. Winner of the 2003 Eureka Science Book Prize and the 2003 Whitley Medal.
Article
This is a review of the structure and innervation of the mechanosensory organ, the push-rod, in skin of the platypus bill and echidna snout. Four receptor types can. be identified in association with push rods in platypus and echidna: (i) central vesicle chain receptors, (ii) peripheral vesicle chain receptors, (iii) Merkel endings and (iv) paciniform corpuscles. Function of the vesicle chain receptors remains unknown. Merkel endings are known to be slowly adapting with irregular discharge (SAI) while paciniform corpuscles are rapidly adapting vibration-sensitive (RA). Recordings made from echidna nose skin have identified both SAIs and RAs. In addition, responses typical of SAII endings (regular discharge) and rapidly adapting, but vibration insensitive, responses were observed. It was concluded that the push rod in monotremes is not associated with mechanoreceptors unique to the group. Skin of the platypus bill and the echidna nose contains erectile tissue. It is conjectured that blood engorgement inflates the skin to facilitate contact between push rods and the external environment. In addition platypus push-rods have a ring of contractile tissue around their tips which, on contracting, restricts mobility of the rod, perhaps when the platypus leaves the water. Possible cooperative roles between electroreceptors and mechanoreceptors are discussed.
Article
Platypuses were observed foraging most frequently in water >1 metre in depth during normal (91.3%) and drought (82.1%) conditions. Mean water depth in the study pools was 1.08±0.66 and 0.86±0.61 metres during normal and drought conditions respectively. The distribution of depths in the study area was significantly different from the distribution of depths where platypuses were observed during normal (Chi2 = 90.2; p < 0.01) and drought conditions (Chi2 = 37.35; p < 0.01). Platypuses were apparently not simply utilising depths in relation to their occurrence but preferring to forage in water deeper than 1.5 metres and avoided depths < 1 metre. Overall distribution in numbers of platypuses observed foraging over different benthic substrate types was not significantly different (Chi 2 = 12.9; p > 0.05) from the distribution of these substrate categories in the study area. However, when the substrates were considered separately, significant preference was shown for cobbled substrate (Chi 2 = 18.4; p < 0.01) and avoidance of gravel (Chi2 = 9.7; p < 0.01). These observations have implications for catchment, stream and riparian management, where activities leading to sedimentation and reduced flushing flows may reduce depths and/or alter the distribution of preferred foraging substrates.