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In early 2000, a team of Filipino and American scientists headed by L.R. Heaney conducted a comprehensive survey of Luzon mammals. Recently, they presented seven new species in the genus Apomys which were identifed from this expedition.  They also proposed a new subgenus Megapomys based on the morphological and DNA data of the 10 already known species and the 7 new ones.

Apomys is a genus of the family Muridae. It is solely found in the Philippines, except in the province of Palawan, the Sulu archipelago, and the Batanes and Babuyan group of islands.  The name Muridae comes from the Latin word mus which means mouse.  Mice from this genus, generally called Philippine forest mice,  are small to medium-sized with tails almost as long as (or even longer than) their heads and bodies.  They are covered in soft, thick pelage that is darker on the back and somewhat white with a moderate orange yellow wash on the ventral (front) area.

Before the Heaney expedition, there were only 10 recognized species under Apomys.  But when the group of scientists studied the morphological differences among mice specimens and their mitochondrial gene phylogeny, they identified 7 more species that were “morphologically distinct and genetically monophyletic.”  They also recognized a fundamental morphological, genetic and ecological dichotomy within the Apomys, prompting them to propose the new subgenus Megapomys.  Thus, based on their findings, the genus Apomys should be split into two subgenera: Apomys and Megapomys.

The subgenus Apomys species includes A. camiguinensis, A. hylocoetes, A. insignis, A. littoralis, A. microdon, A. musculus and several more still awaiting descriptions.

Megapomys includes four known species (A. abrae, A. datae, A. gracilirostris and A.sacobianus) plus the 7 new reported species (A. aurorae, A. banahao, A. brownorum, A. magnus, A minganensis, A. sierrae, and A. zambalensis).

The name Megapomys is a combination of three words: the Greek word megas which means large, the word apo which in Philippine local languages means grandfather (incidentally, Apo is also the name of the Philippines’ highest peak), and another Greek word – mys – which translates to mouse. Mice from the Megapomys are larger and more ground-dwelling than those of the subgenus Apomys.  They are all found in Luzon except for one species that lives in Mindoro. They thrive on lands with elevations that are at least 1000 meters. Some species have even been seen on Mount Pulag (~2900 meters), the highest mountain in Luzon.

A general description of each of the new species is described in the proceeding paragraphs. (For more detailed descriptions, please refer to the journal article cited at the end of the entry.)


Apomys aurorae

Named after the province of Aurora where the species was spotted, this mouse possesses a back pelage that is “rich, rusty reddish-brown, with medium-gray underfur.” The front pelage is “somewhat paler at the base, with the tips either white or white with a pale orange yellow wash.” Its long tail is sharply bicolored. The ventral side of the tail is “usually white, but some individuals have scattered dark hairs and darkly pigmented scales.”

 

Apomys banahao (Courtesy: Heaney, L.R. et al, Fieldiana Life and Earth Sciences, Number 2:1-60. 2011, Drawing by Velizar Simeonovski, The Field Museum)

Apomys banahao

This species lives on Banahao, a mountain in the Quezon Province. The mice have relatively short tails, approximately 86 to 103  percent of their head to body length.  The back pelage is “soft, dense and moderately long; it is dark brown, slightly paler laterally, with slight rusty tints.” The front pelage is “dark gray at the base and white washed with pale ashy-gray at the tips.”

“The ears are darkly pigmented. Dark brown pelage covers the lower forelimb and about half of the posterior portion of the forepaws; pelage is present as a dark brown area of variable size on about the center of the dorsal surface of the hind foot, with white fur both anterior and posterior. The hind feet are pigmented ventrally. The tail is sharply bicolored, with the dorsal surface dark grayish-brown and the ventral surface nearly white.”

Apomys brownorum

Found in Zambales and named after Barbara and Roger Brown, long-time supporters of mammalian diversity research, this mouse species is the smallest among the mice from the subgenus. Their back pelage is “soft, dense, and moderately long; it is a rich dark brown, sometimes with rusty orange tints between the eye and pinna (earlobes) and below the pinna and along the lower margin of the back pelage. The front pelage is dark gray at the base, with grayish orange yellow tips.” The back surface of their tails is dark grayish brown while the ventral surface is almost white.

Apomys  magnus

This is the largest species of Megapomys; hence the name magnus. Its head-to-body length averages 147 mm, and its weight is between 98 and 108 grams. Some grow up to 128 grams with tails that are 96 to 99 percent of their head-to-body length. Its pelage is moderately long and dark brown with conspicuous dark tips and few orange or yellow highlights. The front fur is “medium gray at the base and white at the tips.” The tail is unpigmented ventrally and dark brown dorsally.

Apomys minganensis

The name was taken from the name of the mountain (Mount Mingan in Aurora) where the species lives. The back pelage is “dark brown with rusty-orange tips on the hairs, lying over dark gray underfur.” The front pelage is “dark gray at the base, with paler tips that usually have an ochraceous wash.” The mice have noticeably small eyes and tails that are “dark brown dorsally (always with some dark hairs) and pigment in the scales ventrally.” Almost all have a small white tip, 1 to 4 mm long, on their tails.

Apomys sierrae

This species is named after the Sierra Mountain range where most of the species occurs. It looks similar to A. aurorae except for a few subtle differences. First, its back pelage has a more reddish tint than the yellowish tint of A. aurorae.  Second, its dark hair extends further down on its forelimbs. The main difference, however, lies in the basicranial carotid (base of the skull artery) circulatory pattern.

Apomys zambalensis (Courtesy: Heaney, L.R. et al, Fieldiana Life and Earth Sciences, Number 2:1-60. 2011, Drawing by Velizar Simeonovski, The Field Museum)

Apomy zambalensis 

Named after the province (Zambales) where most of the specimens are found, this mouse is the second largest known species in the subgenus Megapomys.  It has one of the longest tails in the subgenus, typically 94 to 100 percent of the length of the head and body. It is “sharply bicolored, heavily pigmented dorsally but nearly white ventrally.” The bright rusty-orange back pelage is shorter and paler than that of most species, while its front fur is “pale to medium gray at the base and white with an ochraceous wash at the tips” that could vary from slight to heavy.  Its ears are large compared to the other species.

As mentioned, the seven new species belong to the subgenus Megapomys, with roughly all of these living in the northern part of Luzon. Such occurrence sets them apart from the Apomys species which can be found almost all over the Philippines. I will leave the geographical pattern of the subgenus Megapomys for my future entry.

This post is based on the first of five papers about mammal diversity in Luzon in the Fieldiana Life and Earth Sciences journal. According to the authors, studies like this show that

not only are many genera unique to the Philippines, but also that many of these genera are in turn members of endemic clades—entire branches of the tree of life that are found nowhere else on earth.[2]

[1] Heaney, L., Balete, D., Rickart, E., Alviola, P., Duya, M., Duya, M., Veluz, M., VandeVrede, L., & Steppan, S. (2011). Chapter 1: Seven New Species and a New Subgenus of Forest Mice (Rodentia: Muridae: Apomys) from Luzon Island Fieldiana Life and Earth Sciences, 2, 1-60 DOI: 10.3158/2158-5520-2.1.1

[2] preface, Fieldiana Life and Earth Sciences Number 2 :v-vii. 2011 DOI: 10.3158/2158-5520-2.1.v.