Let’s talk about rats … cute native Australian ones …

Fig. 1. Chicago from the John Hancock building (Photo: T. Rymer)

 

Moving on to Blog 7, we’ll be taking a different view from this month of July. We’re more than half way through the year right now, and I’m writing this from the gangster-ridden, speak-easy city of Chicago! (Figure 1). I thought I would take a bit of time to talk about some of the work we’ve been doing on native Australian fawn-footed mosaic-tailed rats Melomys cervinipes (Figure 2). There will hopefully be lots more of this to come in the future.

For starters, I thought I’d take a bit of time to introduce you to this little rat. I coordinated a group of postgraduate and honours students to collate data from a variety of studies into a single work representing the biology, ecology and life history of this species, which we published as a species account in the journal Mammalian Species. We presented a taxonomic account at the species level, providing a species diagnosis and general characters description. We also provided notes on the distribution and fossil record accounts. Finally, we collated information on the form and function, ontogeny and reproduction, ecology, behaviour, genetics and conservation of the species.

Fig. 2. Female fawn-footed mosaic-tailed rat (Photo: T. Rymer)

The species belongs to order Rodentia, family Muridae, sub-family Murinae, tribe Uryomyini. The species was first described by Gould in 1852, and placed in the genus Mus. The specimen was a female, and it is the designated lectotype. The type locality was named as Stradbrook Island (Figure 3) in Moreton Bay, Queensland, Australia. The first occurrence of the current name combination is recorded by Thomas in 1922. The genus Melomys comprises 21 species, of which three are native to Australia. A 4^th species, Melomys rubicola was declared extinct in 2014. No subspecies are recognised within M. cervinipes. The generic name, Melomys is derived from the English Melanesia, indicating the wide distribution of species from this genus, and the Greek mys for mouse. The species name cervinipes is from the Latin cerv for deer or fawn and pes for foot, referring to the light colouring (fawn) of the feet.

Fig. 3. Stradbroke Island, Australia

Melomys cervinipes is small, light grey-brown to russet brown (Figure 2), although colour is highly variable and can change with age, with a white to cream ventral surface, a brown to black tail, and light fawn-coloured feet. Young animals are often a uniform light grey. The fur is soft, fine, and long, and dark whiskers are conspicuous on the muzzle. The ears are short, rounded, and dark grey to black, and the eyes bulge conspicuously. The tail is naked, with the scales arranged in a mosaic-like pattern, interlocking with little overlap, with short hairs, and is approximately equal to the head–body length. The tail is partially prehensile, with the tip capable of curving round objects to potentially provide support. The hind feet are long and wide. Average body mass is 72.9 ± 12 g, average head–body length is 133.5 ± 12.7 mm, average tail length is 142.6 ± 10.9 mm, average hind foot length is 27.5 ± 0.8 mm and average ear length is 18.3 ± 1.6 mm.

Distinguishing this species from its sister taxon Melomys burtoni in the field is challenging. However, some techniques have been used, including counting the number of tail scale rows (13 vs. 14-15), and length of 1^st and 5^th inter-digital pads (1^st = > 2.3mm; 5^th = > 1.7mm indicating M. cervinipes). Dentition provides a more accurate estimate, but is not possible for living wild animals.

In the next blog, I’ll continue to describe the basic biology of this fascinating little rat.

 

You can read more about my research in my publications, listed on my blog. You can also find me on ResearchGate, the James Cook University website and Twitter.

The snail moment you’ve been waiting for …

Welcome to Blog 6, and yes, it’s June. Time marches ever onwards, and we’re half way through the year! Today is the day you’ve been waiting for. The day when I’m going to tell you all about Stephen’s master’s thesis. Thank you for your patience, but the long wait is finally over. Welcome to the discussion of “A classical taxonomic revision of Seraphsidae Jung 1974 (Gastropoda) using a pluralist approach to species assessment”.

Stephen’s thesis demonstrates that a “pluralistic approach to classic taxonomic practice can lead to increased cladistics resolution in a clade, including the recognition of new taxa at all nomenclatural levels”. Okay, so firstly, what is a pluralistic approach? Taxonomists and systematists have a tendency to name species based on particular species conceptions, such as the biological or phylogenetic species concepts. However, often the actual description of the species is not based on that conception. For example, many species are often described based on morphology, but the concept used to define them is based on reproductive compatibility. Pluralism allows a species to be described using multiple concepts, without the need to apply a particular definition that would be limiting. This leads to increased flexibility, and allows for use of all available evidence, rather than limiting the description to only a single kind (e.g. morphology), which often does not match the conception that was used to theoretically distinguish the taxa.

Fig. 1. The fighting conch Strombus pugilus

Stephen’s thesis had three aims: firstly, Stephen wanted to divide the Stromboidea into distinctive evolutionary crown clades using morphological evidence. The intention here was to reinstate the historical understanding of the internal cladistics relationships. A crown clade is defined based on living taxa. The first clade was easy, which is called the Neostromboidea. Animals in this clade contain taxa more closely related to Strombus pugilus (Fig. 1), Terebellum terebellum and Tibia fusus than members belonging to the Struthiolariidae and Aporrhaidae (Fig. 2). The other remaining members of the Stromboidea, the Struthiolariidae and the Aporrhaidae. Defining the other clade in its entirety is, currently, problematic as it would create meaningless ranks.

Fig. 2. The pelican's foot snail Aporrhais serresianus

Stephen’s second aim was to complete an alpha-taxonomic revision of the group defined by Jung (1974) known as the Seraphsidae using a pluralist approach to species conception. I should point out here that he looked at fossils. He first had to compile a list of all the defined taxa. Now this sounds easy, but in reality he had to look for all the synonyms too, so it made it quite a lot of work. He then had to reassess the validity of the synonyms using all available evidence, including morphological variation, historical distribution and temporal positioning. If the named synonymic species could not be validated in the literature, it was not included. Only those with a description that enabled clear resolution of the original author’s intent when describing the species were included. Once he had done this, he had to establish a set of characters for placement in a character state table. He then drew a phylogenetic tree that formed the basis of the internal resolution within the clade (Fig. 3).

Fig. 3. tnt generated maximum likelihood cladogram showing internal cladistic relationships within Seraphsidae Jung 1974 (Taken from Stephen's thesis)

Finally, Stephen’s third aim was to resolve the infrageneric relationships within the Seraphsidae using morphological cladistics. Simply put, what Stephen found here was a need to differentiate and organise this subclade into distinctive inclusive clades that provided an improved understanding of the evolutionary patterns within the group. The first clade represents the Neoseraphsinae nomen novem, with an involute terminal growth pattern. The second clade represents the Neoterebellinae nomen novem, with an evolute terminal growth pattern. Why is this growth pattern important in an evolutionary sense? Because it is related to an essential life history characteristic relating to burial, where the evolute pattern enables detection of burial. That all the Neoseraphsinae nomen novem are extinct indicates that this slight change in shell pattern in the Neoterebellinae nomen novem may have provided an evolutionary advantage, where burial detection may have allowed for additional protection from predation.

The most important message from Stephen’s thesis is that using a pluralistic approach can improve our understanding of internal cladistics relationships in evolutionary trees, and how that can then be reflected in the nomenclature.

You can read more about my research in my publications listed on my blog. You can also find me on ResearchGate, the James Cook University website and Twitter.