20th International Congress of Arachnology

203

DENVER MUSEUM OF NATURE & SCIENCE

REPORTS

No. 3, July 2, 2016

with a two year life span and high reproductive capacity

can set the stage for large, dense populations where intra-

specific competition for prey and territory may be intense.

Cellar spiders are able to autotomize limbs (to escape a

predator or a bad molt), but are unable to regenerate

lost limbs. Thus, losing a leg as a juvenile is likely to

incur lifelong costs. We tested the effects of competition

and autotomy on survival and development in juve-

nile

P. phalangioides

, housed singly or with a partner

(either a sibling or non-sibling) between the third and

fourth molts. Treatments for this experiment were: 1)

autotomized-Intact paired siblings, 2) autotomized-Intact

paired non-siblings, 3) intact-intact paired siblings,

4) intact-intact paired non-siblings, 5) single intact

individuals, and 6) single autotomized individuals. In

each treatment with only one spider, 11 of 16 survived to

complete the fourth molt, but of the survivors, three had

to autotomize one or more legs to escape a bad molt. In

treatments with a lone spider, mortality was confined to

times when molting was occurring. Pairing with another

spider, introduces the risk of cannibalism on top of an

already challenging transition. Cannibalism rates were

high in all paired treatments and in the paired Autoto-

mized-Intact treatments; spiderlings missing a leg were

more likely to be cannibalized by their intact partners.

These results indicate that whereas autotomy is likely

helpful to juvenile spiders in escaping a bad molt, it also

reduces their ability to compete with conspecifics.

Keywords: cellar spiders, autotomy, competition,

survival

Oral presentation

Pre-Pleistocene geological events shaping

diversification and distribution of primitively

segmented spiders on East Asian margins

Xin Xu

1,2,†

, Fengxiang Liu

, Jian Chen

, Hirotsugu Ono

Ingi Agnarsson

5,7

, Daiqin Li

3,†

, Matjaž Kuntner

2,4,5

College of Life Sciences, Hunan Normal University,

Changsha, China;

Centre for Behavioural Ecology

and Evolution, College of Life Sciences, Hubei

University, Wuhan, China;

Department of Biological

Sciences, National University of Singapore, Singapore

Evolutionary Zoology Laboratory, Biological Insti-

tute ZRC SAZU, Ljubljana, Slovenia;

Department of

Entomology, National Museum of Natural History,

Smithsonian Institution, Washington, D.C., USA;

Department of Zoology, National Museum of Nature

and Science, 4-1-1 Amakubo, Tsukuba-shi, Ibaraki-

ken 305-0005, Japan;

Department of Biology,

University of Vermont, 109 Carrigan Drive, MLS-316,

Burlington, VT 05405 USA

xuxin_09@163.com

Phylogeographical research in the East Asian con-

tinent and islands (East Asian Margins, or EAM)

suggests predominant Pleistocene over-water dispersal

events from continent to islands, but more ancient

biogeographical patterns in EAM remain obscure. We

explored biogeographical histories and population

genetic structures of the primitively segmented spiders,

Heptathela

and

Ryuthela

(Liphistiidae), broadly

codistributed across EAM islands. Time-calibrated

phylogenetic, biogeographic and population genetic

analyses were performed. Dating analyses suggest

that i) phylogenetic origin of

Heptathela

Ryuthela

is estimated at 26.6–18.4 Ma (95% HPD) when EAM

islands became separated from the continent, ii) the

crown ages of

Heptathela

(18.0–10.7 Ma) and

Ryuthela

(17.8–8.7 Ma) coincide with the formation of Japan

Sea and Okinawa Trough respectively, iii) a split within

Ryuthela

(13.9–6.0 Ma) coincides with the opening

of the Kerama Gap, but a split within

Heptathela

(18.0–10.7 Ma) pre-dates the formation of the Tokara

Gap, iv) speciation within

Heptathela

and

Ryuthela

is relatively recent (6.0–0.3 Ma). Population genetic

and demographic results suggest interrupted gene flow

within and among islands, with most species exhibit-

ing stable past populations. Our results corroborate

predominantly vicariant origins of genera and species,

and suggest total lack of overwater dispersal in these

sedentary spiders.

Keywords: biogeography, continental islands, dispersal,

Kyushu, phylogeography, Ryukyus, vicariance

International Congress of Arachnology