Hybridisation and Invertebrate Hosts - Two Neglected Aspects of Pest Plants in South-Eastern Austral

2007·1.7 MB·English

by  Randall W Robinson

Biodiversitysymposium
Webb CJ, Sykes WR and Garnock-Jones PJ (1988) WidmerA,Schmid-Hempel P, EstoupAandSchollA
Flora ofNew Zealand. Volume IV. Naturalised (1998) Populationgenetic structure andcolonization
Pteridophytes, Gymnosperms, Dicotyledons. (Botany history ofBombus terrestris s.l. (Hymenoptera:
Division, Department ofScientific and Industrial Apidae) from the Canary Islands and Madeira.
Research:Christchurch) Heredity81 563-572.
WhelanRJ, Brown CLand FarrierD (2004)The pre- ,
cautionary principle: what is it and how might itbe
applied in threatened species conservation? In
Threatenedspecies legislation: is itjustanAct? pp
49-58. Eds P Hutchings, D LunneyandC Dickman. Received5October2006;accepted18December2006
(Royal Zoological Society ofNew South Wales:
Mosman,NSW)
Hybridisation and invertebrate hosts - two neglected
aspects ofpest plants in south-eastern Australia
W
Randall Robinson
VictoriaUniversity,FacultyofHealthEngineeringandScience,
StAlbansCampus,POBox 14428,MCMC,Victoria,8001.
Abstract
Many ofthe threatstoournative flora, includinghabitatdestruction, weed infestations, rabbits, are
glaringly obvious. Hybridisation between native and ‘introduced’ species and introduced plant
species acting as hosts for introduced pests are two threats that are generally overlooked by the
casual observer. Examples are given ofthese two threats to our native plants. The implications of
hybridisation and introduced plantsactingas hostson the long-term survival ofournatural heritage
arediscussed.(The VictorianNaturalist,124(2),2007, 117-122)
Introduction
The impact of introduced plants in weeds on natural ecosystems, the potential
Australia has gained national attention of loss of biodiversity values or the impacts
late, being ranked as one of the highest on human health, most notable on hay
risks to both economic and biodiversity fever sufferers (CRC for Australian Weed
values. The Co-operative Research Centre Management2003).
(CRC) for Australian Weed Management It is estimated that there are 2700 natu-
estimates that the cost ofweeds to agricul- ralised plant species in Australia, many of
ture alone is in the vicinity of $4 billion which were deliberate introductions for
per year (CRC for Australian Weed agricultural or ornamental use (Muyt
Management 2003). This figure does not 2001). Three hundred and seventy ofthese
take into consideration the impact of species are now of critical importance
Fig. 1.Pittosporumbicolor(Left),Pittosporumundulatum(Right)andhybrid(Middle).
Vol. 124 (2) 2007 117
Biodiversitysymposium
(declared noxious in various states of what happens when these plants occur in
Australia) and the focus ofmajor control the ‘wild’? Robin and Carr (1986) high-
efforts (Thorp and Lynch 2000). In lighted the issue of hybridisation between
Victoria alone, there are over580 taxa that indigenous and introduced speciesand pro-
are listed as majorthreats to either agricul- vided 19examples from thegeneraAcacia
ture ortheenvironment(DSE 2006). There Coprosma Epilobium, Grevillea,
, ,
is a range of national and state pro- Nicotiana and Pittosporum. Twenty years
grammes to address the problem ofweeds, later, hybridisation between indigenous
the most notable being the Weeds of and introduced plants still receives little
National Significance Programme and the attention but would appear to be an even
Weeds and Pests on Public Land Initiative. greater risk than originally thought. A few
This latter initiative is funded to the value examples may help to illustratethispoint.
of$14 million over a period offour years Banyalla Pittosporum bicolor is a small
(DSE2006). nativetreethatoccurs in damp forest in the
Assessment ofthe impacts on biodiver- higher rainfall areas ofVictoria, generally
sity can be particularly hard to quantify, at higher elevations (Otways, Central
especially in an economic sense. However, Highlands, Central and East Gippsland)
the direct threats on particular plant, ani- New South Wales and Tasmania.
mal and vegetation communities can be Conversely, Sweet Pittosporum
noted. The Victorian Flora and Fauna Pittosporum undulatum is a large under-
Guarantee Act 1988 (FFG), has the provi- storey tree ofthe lowlands originally con-
sion for the listing ofpotentially threaten- fined to rainforest gullies of Victoria
ing processes (PTPs). It is interesting to (South and East Gippsland), New South
note that ofthe 36 presently-listed PTPs, Wales and Queensland. The desirability of
fivedirectly implicateweed invasions: P. undulatum, for garden use, led to its
1. Invasion of native vegetation by introduction to gardens throughout
BlackberryRubusfruticosus spp. agg. Australia and indeed warmer parts of the
2. Invasion ofnative vegetation by ‘envi- world, soon after colonisation. The first
ronmental weeds’ record ofhybridisation between these two
3. Introduction and spread ofSpartina to species was not recognised as a hybrid
Victorian estuarineenvironments when Morris and Curtis (1974) described
4. Spread ofPittosporum undulatum in the species Pittosporum undulatum var.
areas outside itsnatural distribution emmettii from Tasmania. Since 1974,
5. Degradation of native riparian vegeta- botanists have recognised the hybrid origin
tion alongVictorian riversand streams. ofthis taxon and found it throughout the
In action statements prepared under the entire range of P. bicolor (Flora
FFG Act 1988, 1 1 vegetation communities Information Service, DSE) (Fig. 1)
and I 1 1 plant species are also considered Silver Wattle Acacia dealbata is one of
directly threatened by weed invasions, the most widespread wattles in Victoria,
with mention in each ofthese action state- New South Wales and Tasmania, generally
ments of weed invasions (DSE 2006). occurring in damp to wet forest and along
Interestingly, it is not only plants that are rivers and drainage lines. Cootamundra
threatened by weed invasions but a range Wattle Acacia baileyana is a small tree,
of animals as well, most notably the naturally occurring in a small, low rainfall
Mountain Pygmy Possum Burramys area around the Cootamundra to the
parvus(DSE2006). Wagga-Wagga area of southern inland
While such direct threats as those listed NSW. LikeP. undulatum,A. baileyanais a
above are commonly cited and are actively very populargarden plant and widely natu-
dealtwith,thereisarangeofotherlessobvi- ralised in south-eastern Australia and sev-
ous and potentially more insidious impacts eral countries throughout the world.
ofpestplantsthatgounnoticedbymany. Hybrids betweenA. baileyanaandA. deal-
bata were first noticed in the early 1980s
Hybridisation
(Flora Information Service, DSE). The
Hybrid plants are the mainstay ofour hor- hybrids between these two acacias have
ticultural and agricultural industries but
inherited characteristics from each parent
118 The Victorian Naturalist
Biodiversitysymposium
Table 1 Listofhybridsbetween indigenousand introduced/introducednativespeciesin South-east-
ernAustralia(Flora InformationService, DSE).
Acacialongifoliasubsp.longifoliaxmucronata
Acacialongifoliasubsp.longifoliaxoxycedrus
Coprosmahirtellaxrobusta
Coprosmaquadrifidaxrepens
Correareftexaxglabra
Epilobiumbillardiarianumxciliatum
Eucalyptusbotryoidesxcamaldulensis
Eucalyptusglobulussubsp.globulusxsubsp.pseudoglobulus
Eucalyptusleucoxylonsubsp.bellarinensisxsubsp.megalocarpa
Eucalyptusleucoxylonsubsp.connataxsubsp.megalocarpa
Eucalyptusnitensxovata
Grevillearosmarinifoliaxvariousspeciesandhybrids
Hardenbergiacomptonianaxviolacea
Hardenbergia‘HappyWanderer’ (comptonianaxviolacea)xviolacea
Leptospermumlaevigatumxmysinoides
Melaleucaarmillarisxericifolia
Nicotianaglaucaxsuaveolens(Nicotianaflindersiesis)
Nicotianaglaucaxvelutina
Pittosporumbicolorxundulatum
Table2.NativeforbgeneraonwhichRLEMhavebeenobservedtofeed. *=verysensitive
Ajuga Kennedia Rutidosis*
Arthropodium Leucochrysum Stylidium*
Brachyscome* Lotus* Swainsona
Craspedia* Microseris* Velleia
Cullen Minuria Wahlenbergia*
Glycine Podolepis Xerochrysum
Goodenia Pterostylis
that make them a cause for concern: from Halotydeus destructor (RLEM) were feed-
A. dealbatatheyhave inheritedthehabitof ing heavily on mature plants of many
extensive clonality (suckering), from A. indigenous species. The feeding of the
baileyana drought tolerance (pers. obs.) RLEM was causing considerable damage
These hybrids can be found growing in a to the mature plants, in some cases weak-
wide range ofhabitats, from damp forests ening them to the pointofdeath orin some
and rivers to dry hilltops, forming large cases preventing flowering. Investigations
vegetatively produced colonies tens of into RLEM revealed that they are a major
metres across(pers. obs.). problem in agricultural crops, reducing
These arejusttwo ofthe increasingnum- recruitment by up to 86% in Lucerne,
ber of species that are found to be hybri- Canola and various clovers (Liu and
dising in bushland areas throughout south- Ridsdill-Smith2000).
eastern Australia. What is the long-term Red-legged Earth Mites were introduced
impact ofthis type of ‘genetic pollution’ into Australia from South Africa in 1914
(Robin and Carr 1986) on our biological (Liu and Ridsdill-Smith 2000).
heritage? In all likelihood, several of our Interestingly, in their home country, they
plants may be hybridised out ofexistence. feed primarily on members ofthe Daisy
In some cases, most notably Grevillea ros- family (Asteraceae) and Pea family
marinifolia ‘Hurstbridge Form’, this (Fabaceae) (Annells and Ridsdill-Smith
already may have happened. Table 1 lists 1994). One oftheir host plants in South
someexamplesofknownhybrids. Africa is the now ubiquitous Capeweed
Arctotheca calendula (Annells and
Weeds as harbourforinvertebrate pests Ridsdill-Smith 1994). The mites cause
mDuernitngosftugdrieasssclaarnridedfoourtbsonintheVircetcoruriita- tvheeryolditdtlestdiapmpalgineg toofClaepaevweeseadnadpasrltigfhrtolmy
(Robinson 2005), it became evident that larger dead patches on leaves where they
the introduced Red-legged Earth Mites
have extracted the contents of individual
Vol. 124 (2)2007 119
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Fig. 2.AcaciabaileyanaxdealbataonadryhillsideatCottles Bridge,Victoria.
cells in the leaf(pers. obs.). The distribu- RLEM. The spread of RLEM-sensitive
tion ofthis pest is generally in south-east- weeds and their dominance ofsome vege-
ern and south-western Australia at eleva- tation types, coupled with infestations of
tions below about 300 m. The distribution RLEM, may be putting enormous pressure
ofthis species coincides with the distribu- on our indigenous forb species.
tion of lowland grasslands and grassy Observations by Neville Scarlett (pers.
woodlands in southern Australia (Lui and comm.) indicate that several ofthe Snout
Ridsdill-Smith 2000). Mites, predatorymitesthat feed on RLEM,
A survey ofplants susceptible to the pri- may be absent from ‘disturbed’ grasslands.
vations ofRLEM carried out by the author Scarlett further observes that many ofthe
revealed that it was not only the agricultur- indigenous species are sensitive to RLEM
al crops and indigenous natives that were and the equally widespread Blue Oat Mite
sensitive. Some ofour most common and Penthaleusmajor.
widespread weeds are sensitive to RLEM The importance ofweed control, coupled
or act as host to the species. Most ofthe with invertebrate control, may be one of
‘thistles’ including Spear Thistle Cirsium the keys to allow the successful recruit-
vulgare and Variegated Thistle Silybum ment and conservation of our indigenous
marianum host large numbers ofthis pest forb species. Table 2 contains a short list
but still seem able to survive and repro- ofsomeofthegenerasensitivetoattack by
duce (pers. obs.). Other species including RLEM.
several of the Chickweeds, particularly
Stellaria media and Cerastium Long-term implications
glomeratum. Shepherds Purse Capsella The hybridisation ofindigenous and intro-
bursa-pastoris, andeven the horticulturally duced species and the hosting of inverte-
desirable Cyclamen species areparticularly bratepestsbyweedscould have long-term
sensitivehosts. implications for the structure and floristics
Light infestations of the above-listed of plant populations. Alterations to the
introduced weed species, which occur in genetic make-up ofpopulations, particular-
even the most intact grasslands and grassy lythechanges broughtaboutbythe mixing
woodlands, would provide harbour for or homogenisation of formerly distinct
120 The Victorian Naturalist
Biodiversitysymposium
Fig. 3. Acacia baileyana
(Left), Acacia dealbaia
(Right) and hybrid
(Middle).
species, may bring about extinctions
of some plants, even some of the
most common species. The physical
and ecological attributes of hybrid
entities, particularly wider ecologi-
cal amplitudes exhibited by the
examples given above, extensive
clonality and larger size may lead to
replacement not only ofthe original
species subject to hybridisation, but
other species as well. In the case of
Pittosporum bicolor x undulatum
,
the hybrid plant has most of the
attributes ofthe introduced parent:
larger size, denser canopy and more
prolific flowering. This will lead to
stronger competition with other
plants, particularly for light and
water. In the case ofAcacia bai-
leyana x dealbata, the strong suck-
ering habit and much widerecologi-
cal tolerances of the hybrid will
allow a wide range ofvegetation
communitiesto be invaded, with the
consequentflow-oneffects.
Genetic ‘pollution’ is difficult to
assess and not readily evidentto the
casual observer. Complete replace-
ment ofthe original genetic entity
with the hybrid may not be evident
until there is a recruitment event.
This may be analogous to the case
ofthe Red-tailed Black Cockatoo
Fig.4.Red-leggedEarthMitesontheundersideofaleaf wheretherewouldappeartobe many
ofShepherds Purse Capsella bursa-pastoris. Necrotic
areasaredamagecausedbyRLEM. individual animals. It is not until
there is an analysis of the age
Vol. 124 (2) 2007 121
Biodiversity’symposium
structure of the population that it is References
realised that there are no young birds and Annells,AJandRidsdill-Smith,TJ(1994).Hostplant
most ofthe older birds are beyond repro- sopfecimeusltainpdliccaartbiohoyndraotfe sruepdplleegmgeendts aefafretchtinmgirtaet.e
ductive age. In the case of Grevillea ros- ExperimentalandAppliedAcarology18,521-530.
marinifolia therewouldappearto be many CRCforAustralianWeedManagement(2003).Killing
plants unti,l one notices that all of the ousnsiofntvlaysiveAusptlraanltisa’sangdreaenwsatyalkferosr:waarcda.llCtoRaCctifoonr
seedlings areofhybrid origin and the older Australian Weed Management, Glen Osmond, SA,
plIannttshaerecadsyeinogforRLunEthMr,iftpyr.edation of the DSmAuEasnt(ara2gl0ii0an6.g)tIhneteernivmirgounimdeenltinaelsiampnadctpsroocfedwuereedssfoonr
seedlings of many ofthe grassland forbs public lands in Victoria. StateofVictoria, Victoria,
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described above. Many of the grassland http://www.dse.vic.gov.au/dse/nrenpa.nsf/FID/-
forb species are long-lived perennials. 5C06524B60919FED4A2567C1001223BF?OpenDo
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recruitment ofthese species but the process managing the environmental impacts ofweeds on
ofdeath and decay ofthe older plants con- public land in Victoria. The State ofVictoria,
tinues apace. One or a few episodic events, FloMrealbaonudrnFea,uAnuastGrualairaa.ntee Act (1988), Parliament of
a particularly bad drought or intense fire, Victoria,Victoria,Australia.
corounlodaebliliimtiynaftoreroelcdreuritpmleannttsw,itlheianvitnhgepliotptl-e FLlioRureadAlIenafgnogdremdaRtieidaosrndthSielrmlvi-itSceme,i(tHDhaSlTEotJyd(e2u0s00d)esFteruecdtionrg) obny
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gation ofthe problem. To date, there is lit- Mutyurte.ARe(c2o0r0d1s)oBfutshheQinuveaednerVsicotfosrioautMh-uesaestumAu5s0t,ra1l-i5a:
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vegetation dynamics in general. Weeds ofNational Significance. National Weeds
Controlling weeds is only a part of the StrategyExecutiveCommittee,Launceston.
solution to achieve what is in fact our pri-
mary goal: the attainment ofhigh quality Received5October2006;accepted25January
sustainableplantand animal communities. 2007
One Hundred and Twenty Years Ago
THE LOCUST PLAGUE.
ACORRESPONDENTat Murtoa, in the Wimmeradistrict, forwardsthe followingnotesonthis
subject:-
"They appearto fly in swarms, in sizevaryingfromafewyardswideto overamile,andofgreat
length, as sometimesthe flightcontinues fromhalfan hourto an hourwithoutthe slightestbreak.
They fly about 20 to 25 feet above the ground, and seem to be ableto sustain themselves on the
wingforalongdistance,and I fancythosewhichrest,exceptforfeedingpurposes,areyoungerand
weakerthanthecompanytheyarein.Theyevidentlycampatnight.1wentoutabouthalf-pasteight
forthe purpose ofcatching some; they were all on the move as soon as they heard me, but only
usedtheirlegs,anddidnotattempttofly. Theydidnotdomuch damagetothewheatcrops in this
district; but the grass paddocks were cleared right offin a day ortwo, sothatthe farmers will be
obligedtoselltheirsheepatonceforwhattheywill fetch,astheyhavenofeedleft”
From The VictorianNaturalist3 p. 131, February 1887
122 The Victorian Naturalist