he Australian continent is renowned for its idiosyncratic flora and fauna and high diversity of endemic taxa (e.g., Eucalyptus, marsupials, and monotremes; Braithwaite RW. 1990. Australia’s unique biota: implications for ecological processes. J Biogeogr. 17:347–354.). Given this diversity, it is perhaps not surprising that Australia is a coveted and productive field site for behavioral ecologists worldwide. The prevalence of some unusual animal behaviors is well documented, such as cooperative breeding in birds, low rates of herbivory, and high rates of pollination by vertebrates. However, other behavioral phenomena, especially those involving deception and exploitation, are also remarkably prevalent in some systems and still require comprehensive treatment. We examine 3 distinct forms of deception in entirely different taxa, cuckoos, crab spiders, and orchids, where there is strong evidence that deception is more prevalent in Australia than in other geographic regions. We offer several explanations addressing environmental conditions, evolutionary isolation, the prevalence of behavioral ecologists, and the research culture in Australia. The aim of this “Idea” paper is to draw attention to intriguing patterns of deception in a limited number of well-studied systems and to generate several testable predictions. It is not intended as a thorough review of all deceptive systems, but we hope to stimulate more research, a systematic review, and further testing in this area.
BROOD-PARASITIC CUCKOOS
Despite being substantially smaller than Africa (one-quarter) or Asia (one-sixth), Australia is home to ~20% of the world’s brood-parasitic cuckoo species (Australia: 12, Africa: 15, Asia ~26 of 57 species in total; Davies 2010). These cheats outsource parental care and have evolved many deceptive signaling strategies to impair host detection including mimicry of host egg and chick colors and calls (Stoddard and Stevens 2010; Kilner and Langmore 2011; Langmore et al. 2011). Not only are brood-deceptive cuckoos more common than expected in Australia, the cuckoo–host relationship seems to differ from other regions. Australian cuckoo–host interactions are characterized by lower rates of cuckoo egg rejection by hosts in comparison to European counterparts (Langmore et al. 2005). Among other factors, Australia’s milder environmental conditions provide hosts with longer breeding seasons allowing multiple clutches, whereas European hosts that are limited to single clutches may be under stronger selection for detection and rejection (Langmore et al. 2005).
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DECEPTION BY CRAB SPIDERS
Crab spiders typically sit on flowers and hunt pollinators. European and American species are renowned for their cryptic coloration against the flower background (Théry and Casas 2002; Morse 2007). Their foraging success depends on being undetectable to the approaching pollinator. Recent work on Australian crab spiders, however, has revealed that they are far from cryptic, reflecting high amounts of UV light, thereby forming a strong color contrast against the floral background (Heiling et al. 2003). The UV component of their body color acts as a deceptive signal that lures both native and introduced pollinators closer to the flower (Heiling and Herberstein 2004; Heiling et al. 2005; Llandres et al. 2011). A multispecies comparison has revealed that deceptive signaling via UV reflection is seemingly overrepresented in Australian species (at least 5 species from 4 different genera). In the intensively studied European species, UV reflection is absent (Herberstein et al. 2009). Similarly, no cases of UV reflection are known from American or African species, and only one report of deceptive signaling via UV reflection comes from India (Bhaskara et al. 2009).
SEXUAL DECEPTION BY ORCHIDS
Sexually deceptive orchids are pollinated by male insects fooled into sexual behavior with orchid flowers (Vereecken 2009; Gaskett 2011; Schiestl 2011). These orchids do not offer a nectar reward and attract pollinators by mimicking the scents, shapes, and colors of female insects (Ayasse 2006; Gaskett and Herberstein 2010; Peakall et al. 2010; Ayasse et al. 2011; Gaskett 2012). Deceptive signaling involves exploitation of their pollinator’s innate sensory biases (Streinzer et al. 2009; Gaskett 2013). Within Europe, sexual deception is largely restricted to only 2 genera: almost all ~255 species of the genus Ophrys and 1 species of Orchis (Paulus 2006; Ayasse et al. 2011; Gaskett 2011, but see Vereecken et al. 2012). In Australia, sexual deception has not just radiated from 1 genus, it has evolved independently at least 6 times, resulting in at least 11 genera and several hundred sexually deceptive species. This represents almost 50% of known sexually deceptive orchid species (Kores et al. 2001; Gaskett 2011).
Based on these 3 unrelated systems, we show that deceptive strategies are well represented in Australia, perhaps more so than expected compared with other regions. In the following sections, we propose several mechanisms that might explain this overrepresentation, including overall species diversity, the prevailing ecological conditions, the isolation and invasion history of Australia, and the prevalent research culture in Australia.
IS THE PREVALENCE OF SOME DECEPTIVE SYSTEMS A REFLECTION OF SPECIES DIVERSITY?
It may be that the diversification of deceptive strategies is a function of overall species diversity. In this case, we expect the overall species diversity of birds, spiders, and orchids to be proportional to the diversity of cuckoos, sexually deceptive orchids, and deceptive crab spiders. Based on a 2009 estimate, Australia holds about 8–9% of the world’s bird diversity (9990 described species worldwide of which 828 occur in Australia; Chapman 2009). The diversity of cuckoos in Australia however is double that of the overall bird species diversity. Similarly, of more than 40 000 described spider species, ~8% occur in Australia (Chapman 2009), whereas almost all examples (5/6 species) of deceptive crab spiders identified so far come from Australia. Finally, the overrepresentation of sexual deception in Australian orchids is clearly not the result of an overall greater diversity or abundance of orchids in general: Australia is home to only ~5% of the world’s orchid diversity (1200 species out of a global total of ~25 000; Dressler 2005; Hopper 2009; Table 1). Overall, species diversity in Australian birds, orchids, or spiders does not offer a strong explanation as to why deception is prevalent in these systems.
Orchid genera with sexual deception, food deception, or providing food rewards in 2 key regions of diversity: Australia and the Mediterranean
DOES DECEPTION EVOLVE READILY IN AUSTRALIA?
Australian environmental conditions
Australia’s dryness, poor soils, and frequent fires explain several biological phenomena including production of nutrient poor biomass (resulting in low rates of herbivory) and abundant nectar and sap (leading to pollination by larger than average animals; Orians and Milewski 2007). It is conceivable that these overriding environmental constraints have led to selection for behavioral strategies that minimize the costs of acquiring or producing resources, such as outsourcing of parental care, and floral rewardlessness (Dafni and Bernhardt 1990; Gardener and Gillman 2001; Orians and Milewski 2007). If this were the case, we would predict that deceptive systems are more common in habitats with harsher climates (dry and poor soil, high frequency of fire), both within Australia and in other regions. However, we have limited information to evaluate this prediction.
The interaction between climate, Australia’s long history of fire, and biodiversity may be factors explaining the incidence of deception especially in orchids. For example, fragmentation of orchid habitat caused by fire regimes may select for gene flow across larger distances, which may be facilitated by the greater outcrossing associated with sexual deception. Outcrossing is also associated with faster seed germination—this may also improve survival through the harsh summer by promoting earlier establishment (Peakall and Beattie 1996; Johnson and Nilsson 1999). Nevertheless, it may be phylogenetic constraints rather than resource limitation that select for the unusual parental strategies of Australian birds, including cooperative breeding (Cockburn 1996). Similarly, deception and rewardlessness in orchids provides outcrossing benefits and is no longer considered an adaptation to resource limitation per se (Jersáková and Johnson 2006). To fully examine the effect of environmental conditions requires investigating the distribution and abundance of deceptive and nondeceptive strategies of orchids and brood parasites across different Australian climate zones as well as similar environmental conditions outside Australia.
Isolation and invasions
Australia’s long history of evolutionary isolation and recent invasions may explain the radiation of deception more broadly. If this is the case, we predict that deceptive species are relatively recent arrivals in Australia that exploit naive endemic receivers. Australia separated from the Gondwanan land mass 35–40 million years ago (Westoby 1988; McLoughlin 2001). This isolation and the favorable Mediterranean and tropical climates have resulted in high levels of biodiversity and endemism (Cowling et al. 1996; Peel et al. 2007). This underlying diversity could provide a wide variety of potential targets for deception. In addition, isolated or island populations are typically more vulnerable to exploitation by invading species (Reaser et al. 2007). The mixing of existing and invading biota can lead to the evolution of new symbiotic relationships (Mooney and Cleland 2001) and this may well include deception.
Following the more recent continental contact between Australia and Asia, there has been frequent invasion by tropical species from Asia (O’Hara and Poore 2000; Murphy et al. 2006). Invading species with the capacity for deception may rapidly disperse and speciate throughout the continent, taking advantage of the relatively naive local species. The success of cuckoos, crab spiders, and orchids may have been the result of such invasions. Australian cuckoo genera are monophyletic and shared with Asia (Sorenson and Payne 2002), tentatively supporting the idea of recent invasions. Australian orchids stem from the independent arrival of 2 closely related subtribes from the Southern Hemisphere tribe Diurideae (Kores et al. 2001). It is unclear whether these orchid subtribes originated in Australia or close to Asia. The biogeography of Australian spiders is unresolved but likely to be complex, consisting of both endemics and recent invaders from southeast Asia (Murphy et al. 2006). To thoroughly test this idea, however, we require biogeographic data on the evolutionary relationships of Australian deceptive taxa.
DOES AUSTRALIA’S INTELLECTUAL AND RESEARCH CULTURE ENCOURAGE DISCOVERY OF DECEPTION?
Interpreting any data on the frequency of an observed phenomenon requires knowledge of potential biases in reporting. It may be that the popularity of certain research areas, such as behavioral ecology in Australia, leads to a higher than expected reporting of charismatic phenomena including deceptive systems.
Behavioral ecology is thriving in Australia given the number of research institutions compared with other nations (Table 2). Over the past few years (2010 and 2011), 8% of all papers published in Behavioral Ecology were authored by researchers at Australian institutions (Simmons 2012). In contrast, 16.5% of papers were from the United Kingdom, which has 3 times as many institutions as Australia. The number of Australian-led papers published in other behavioral journals were similar over the same time period (Animal Behaviour: 7.7%; Behavioral Ecology & Sociobiology: 7.5%; Source: Web of Science, accessed 6 May 2013), suggesting that the observed publication data are not necessarily a reflection of the composition of editorial boards (Behavioral Ecology: 6 Australian-based editors out of a board of 28, Animal Behaviour: 2/32 editors, and Behavioral Ecology & Sociobiology: 4/41 editors).
Descriptives of the higher education environments in Australia, Europe, United Kingdom, United States of America, Canada, and Japan, indicating Australia’s surprisingly large proportion of behavioral ecologists and consequent contribution to the journal Behavioral Ecology given the relatively few research institutes
The relatively recent research culture in Australia (Table 2), compared with Europe, United Kingdom, and the Americas, may also encourage natural history–based research (e.g., Shine 1994). Long-term data sets are not yet available for Australian study systems and this may stimulate researchers to think creatively and pursue nontraditional questions such as the lack of monogamy in passerines (Double et al. 1997), slave making of unrelated juveniles for cooperative breeding in choughs (Heinsohn 1991), traumatic insemination and penis fencing in hermaphrodites (Michiels and Newman 1998), and reversal of sex roles in nuptial feeding (Arnqvist et al. 2003). Discovering and characterizing deceptive systems requires similarly innovative approaches, and a peer environment that supports investigation into the obscure and the cryptic. However, we require more thorough analyses of the number of publications on deceptive and nondeceptive systems, and a measure of how often papers report on the same deceptive system, to fully evaluate the potential of publication bias.
In conclusion, we show that in 3 unrelated systems, deceptive species are more prevalent in Australia than in other world regions. We find no support that the diversity in deception is a reflection of overall species diversity. However, it is likely that the combination of climate and isolation favors the evolution of deception in Australia and that the academic environment favors studying these systems. Thus, we argue that Australia provides a “perfect storm” for deception.